Is there a way to check all available snipMate snippets? Like the i <c-r><tab> does, but with a little more information?
I am curious about:
Some tool that allows conversion to HTML would be fantastic, but an in-vim trick would be cool too :)
No.
Frankly, I don't see that option as being terribly useful altogether. For the purpose of snippets is that they're chunks of text that get inserted upon typing a short word, so you don't have to type them in full. They're something you know by heart, just don't want to type over and over again.
They're not code blocks in a way of semi-visual-programming, where you just insert predefined blocks. Which is what you seem to be aiming at.
The easiest way to check out snippets is to go through the snippet files.