Gear to protect against hand injury in a crash

Maybe try Downhill Mountain Biking gloves. Downhill doesn't suffer the same weight considerations as road cycling, so the gear is generally much tougher and designed to offer protection in some pretty terrifying crashes. The best pair I had were designed with gel-pads at the heel of the hand, which cushioned any impacts...of which I had a few.

Snowboarding wrist guards are an option also, they contain a hard plastic strip running up the bottom of the forearm, however I've never tried cycling in a pair so I'm not sure how comfortable they would be. They'd possibly prevent wrist injury from hitting the floor.

Consider tyre choice when it's snowy or during periods of leaf-fall.

Thankfully I never ride without gloves. The light weight gloves with padded leather in the palms is all you need - they are cheap, comfortable and effective - what more could you ask for. I had a crash after my bike was tampered with and the front wheel fell off. I am a programmer, and although I emptied the company first aid kit of dressings, and could not walk properly or bend my elbow for days, I could still type. Had I not been wearing gloves, I would have been off work for weeks.

As I see it, if you damage the leather enough to make the gloves unserviceable, and walk away - keep walking - straight to you lottery shop. Leather is tough and slide - in my case the gloves, which took the full impact of my fall, had no visible damage - unlike my shoulder, elbow and hip....

Wearing big heavy gloves might protect you hands, but downhill riders and motorcyclists that wear these also wear full face helmets and body armour - unless you do the same you will come off and although your hands will be fine, the rest of you won't be.

Any bone damage is a problem - if you don't want it, don't fall off. You can learn to fall to minimize injury - downhiller riders are the masters of this, question is - can you be bothered as the only real way to learn is to do it.... You could wear body armour but its no guarantee.....

Edit: Since writing this many years ago, I have taken up Martial Arts with my children (I am over 50). The techniques taught have helped enormously in a couple Mountain biking falls I have had, including one where I went 'over the bars'.

There is plenty of advice about gloves under the Gloves tag. See especially the question "What's the purpose of cycling gloves?" and one of the answers. From which you see that I recommend ordinary cycling gloves. Your purpose is their purpose.

But I suggest that while you should be wearing gloves, you also should pay attention to how you ride, and where you ride.

On a bike, as you have discovered, you are vulnerable. Ride according to the conditions. Commuting is actually quite dangerous, because we tend to ride in a wider range of conditions: wet, windy, icy, leafy, greasy, heavy traffic, poor visibility, pedestrians, skateboarders, rollerbladers, other cyclists. Every one of those should cause us to change our riding to match, usually by slowing down, sitting up, and looking for options.

As a cyclist, I always think I have to take 100% total responsibility for my safety - because it's me who'll get hurt.

Every time you have (or had) an incident (don't call them accidents), think through what you could have done to avoid it. Autumn leaves will fall in Autumn. Pedestrians will walk out when you can't see them (because they can't see you). Cars will change lanes without indicating.

Sounds like I must ride like a little old lady, but the opposite is the case. However, in the last 30 years I've had only 3 crashes. In retrospect, I realized that each one could have been avoided by paying more attention to the conditions and situation.

Also rethink those incidents where you didn't crash. Yesterday, I took a downhill negative camber corner faster that I ever have. I suddenly found I was sliding - my front tire had developed a leak and didn't have enough grip anymore. Fortunately, there was no oncoming traffic, I stayed upright, and was able to stop. But I'm thinking - what were the warning signs? I was already taking a risk - how could I have reduced it?

Take care out there and ride according to the conditions.

Answer Your are asking for a technical solution to a people problem.

Go to an Aikido class for a month, and learn how to fall.

If after that you still feel unsafe, add elbow protectors to your knee pads.

Also ride an MTB and fall a lot onto soft ground.

EDIT: Years later, I still uphold this opinion. Do see the last paragraph of the accepted answer.