• Italy: www.igmi.org/geoprodotti

I hope to add more details here and add it to the wiki once I try them out in practice shortly.

Denmark, including Faroe Islands and Greenland (also Sweden): ScanMaps

Many different scales, ages and media as well as customized, personal maps printed and sent to you. Site is in Danish, but you can change to English. The official government institution for Geo-data links to this (commercial) site for printed maps.

Topographic, Digital maps are available for download as TIFF images (for free); resolutions 1:25.000 - 1:1.000.0000 at kortforsyningen.dk (site is unfortunately only in Danish)

Europe

• Austria: The Bundesamt für Eich- und Vermessungswesen (BEV, "Federal bureau for metrology and surveying") publishes the ÖK50 series in scale 1:50000, covering the whole country. Each map has a four-digit code, and for each (blue) ÖK50 map, there are two (green) ÖK25 maps in 1:25000 for the east and west half carrying the same number (XXXX-Ost and XXXX-West). The maps are available in larger bookstores. Marked trails and huts are indicated on the maps. There's an online viewer for all their data. The alpine association (ÖAV) also has a series of hiking maps for the alps, produced in cooperation with the BEV and the German alpine association (see Germany).

• Belgium: The Nationaal Geografisch Instituut/Institut géographique national has multiple series of non-congruent, numbered maps covering the country, called topo10, topo20/25 (blue), and topo50 (red). The latter two include marked trails.

• Denmark, including Faroe Islands and Greenland (also Sweden): ScanMaps. Many different scales, ages and media as well as customized, personal maps printed and sent to you. The official government institution for Geo-data links to this (commercial) site for printed maps. Topographic, Digital maps are available for download as TIFF images (for free); resolutions 1:25.000 - 1:1.000.0000 at kortforsyningen.dk (site is unfortunately only in Danish)

• Finland: Maanmittauslaitos (MML, "National land survey") doesn't itself provide a series of paper maps, but their data is available online with tools for buying on-demand printed and PDF maps. Furthermore, they provide for free high-resolution scans of old printed map series. There is, however, the GIS company Karttakeskus, who have a series of numbered and congruent topographical maps (maastokartta) in 1:50000 and 1:25000, covering the country. In outdoor shops you'll find Calazo maps, which cover some national parks and famous trails.

• France: The Institut national de l’information géographique et forestière (IGN) publishes Cartes de randonnée with a Serie bleue of 1:25000 maps of all regions. Marked trails are indicated.

• Germany: There is an official system of Topographische Karten ("topographical maps" -- TK, or nowadays DTK for Digitale Topographische Karten) in several scales with congruent and numbered sheets, but it is somewhat decentralized. The interesting scales, TK25 and TK50, are managed and published by the respective federal states' surveying agencies. They can be bought at the state agencies (eg. Niedersachsen; sometimes, printed on demand) or at bookshops. For hiking in the German alps, there is a series of maps published by the alpine association.

• Greece: Γεωγραφική Υπηρεσία Στρατού (Γ.Υ.Σ., "Hellenic Military Geographical Service") does have a website (optimized for IE 6 :)) with a shop where maps of different scales can be bought. As far as I understand, there is a grid of numbered 1:5000 topographical maps over the whole country, and some other named maps in more usual scales are available; for selection, they have an interactive map.

• Hungary: The Department of Geodesy, Remote Sensing and Land Offices has official topographic maps, but they are not free (and their site has an invalid certificate). turistautak.hu is a non-profit portal which has a community-sourced interactive map with marked trails and other outdoors info. When looking for printed maps, the series by Cartographia and Szarvas térképek are the most widely used ones.

• Iceland: Landmælingar Íslands, the National Land Survey of Iceland, doesn't itself publish maps, but have their data viewable online. However, there are printed hiking maps with blue cover, which you will find, outdoor shops and tourist infos. They are published by Mál og Menning, a book shop in Reykjavík. These maps don't cover the whole of Iceland, but only some "interesting" regions (eg. Laugavegur), in varying scales (usually 1:50000 or 1:100000), and show marked trails.

• Ireland: The Ordnance Survey Ireland is Ireland's national mapping agency. They are the responsible authority for all maps relating to Ireland. They offer road maps, professional mapping data for businesses, and maps for the outdoors.

• Italy: The Istituto Geografico Militare (IGMI, "Military Cartographic Institute") has several series in different scales, which one can view and buy from their website.

• Luxembourg: Le Géoportail National Du Grand-Duché De Luxembourg provide the various maps for Luxembourg. You can find them in various scales, such as 1:20000, 1:250000 and 1:5000. You can print the maps and modify them them online. The maps are available in English, German, French and Luxembourgish.

• Netherlands: Topografische Kaart Nederland van het Kadaster. The maps are readily available in 1:25000 and 1:50000 scale, as the basic map and with specialist additions like for cycling or walking, (also) from other publishers. Other scales are available as well.

• Norway: Kartverket, the Norwegian mapping authority, doesn't provide a (paper) map series, but all their data is available online, including a map viewer. However, there are two series published by Nordeca, which are recommended by DNT (the Norwegian alpine association) and available their stores. The Norge series covers the country in scale 1:50000, while Turkart are developed in cooperation with DNT and come in several scales for "interesting regions". The latter include marked trails and huts.

• Spain: The Instituto Geográfico National (IGN) publishes a Mapa Topográfico Nacional series in two scales, MTN25 and MTN50. Each MTN50 map has a number (X) and is divisible into 4 MTN25 maps (X-1 to X-4). Both series are also available in electronic form.

• Sweden: Lantmäteriet is the "official" mapping agency. They provide 1:50000-scale topographic maps (Terrängkartan) for most of the country, except the mountains in the northwest which are covered by the 1:100000-scale fjällkartan. There also some smaller-scale maps. However, their production of paper maps will cease this summer. 50k and 10k-maps are available as PDF, and the data corresponding to the 50k maps is available as open data.

• Switzerland: Swisstopo, the Swiss federal office of topography, provide multiple (numbered and congruent) series. For one, there are the national maps in 1:25000 ("brown" series) and 1:50000 ("green" series) covering the whole country. Switzerland has a huge network of waymarked hiking trails, so swisstopo also publishes a "yellow series" of hiking maps in 1:33333 and 1:50000 scales, which use the 1:50000 base map with the hiking trails marked in colour. Unfortunately, swisstopo itself does not publish a 1:25000 series showing the hiking trails, but various third party providers do. Such maps can generally be found at local bookshops and tourist offices. The whole data are also viewable for free online, including option to download a tile for offline use and extensive geoinformational data.

• UK: The Ordnance Survey publishes two series covering England, Wales, Scotland and Isle of Man: Explorer in scale 1:25000 (numbered OL + digits), and Landranger (just digits) in scale 1:50000. Their sheets are not necessarily congruent.

  Ordnance Survey of Northern Ireland cover the country at 1:50000 (Discoverer series) and popular recreational areas at 1:25000 (Active series).

  Harvey Maps is an alternative mapping provider offering 1:25000 and 1:40000 maps of the main hiking areas. OS and Harvey maps differ in style and both are widely sold in the UK.

North America

• Canada: National Topographic System Maps

• United States: The official publisher of topographical maps in the United States in the United States Geological Survey. They have both 15 and 7.5 minute maps as well as historical topographical maps. It is possible to download the maps for free, or some outdoor shops will sell the paper maps.

Oceania / Australia

• Australia: while the government has a dedicated webpage with several resources, HEMA maps is the provider used for navigation and orientation. It frequently appears as the maps to be used in insurance polices and car-rental agreements.

• New Zealand: The government in the form of Land Information New Zealand supplies topographic maps, aerial imagery and orthophotography and a range of cadastral information. The current map series is Topo50, on a scale of 1:50,000, which covers the main islands of New Zealand and the Chatham Islands. Larger scale maps in the form of Topo250 (1:250,000) are also available. Maps in digital format are freely available under Creative Commons Attribution 4.0 International Licensing, and are available to download here. Large public libraries often contain collections of the more recent topographic maps as well as some older forms for free perusal and photocopying. Paper maps can be purchased from most book-stores and information points, as well as many outdoors stores. Some organizations, particularly hunting clubs also provide digital maps for free.

South America

• Peru: http://www.lib.utexas.edu/maps/topo/peru/