What is the plural form of "Software"?

I avoid that by saying "software products".

I would use programs instead:

There are various video conversion programs in the market.

Software, in my opinion, is better used as the general concept (as opposed to hardware, say). All of the programs on my PC are software. My hardware consists of a CPU, memory, fans, screen, etc.

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Oh, and also I can't resist to refer to the recently common half-joke codes (as in "plz show me the codes" so frequent in certain programming forums).

Just a note to clear up any confusion: I believe the answer provided by RegDwight is correct; but I also want to point out that because the word "software" is uncountable, there is no such thing as a "plural form."

What I mean is this: don't misinterpret the accepted answer to imply that the following sentence is correct:

The company Microsoft produces many software.

The above is problematic for the same reason that the following sentence is problematic:

My bottle is full of many water.

So again: to answer your question directly, there is no plural form. Software is like water; you can have "a lot" of it, but you can't have "many" (or "dozens", or "hundreds", etc.) of it. You can, however, as the other answers have already indicated, have "many pieces of it" (just like you can have "many bottles of water").