There are a lot of open source licenses. Even if you look at only the OSI approved ones, that’s still a list of 67. And, of course, they are all different in subtle (and not-so-subtle) ways. Can you keep all the small details straight in your head? I know I can’t. That’s why I just made a quick reference page:
It focuses on just a few commonly used licenses (at least from what I can see), but covers more criteria than the other comparisons I’ve seen so far.
I hope it will be useful for you.
Update 3rd April 2011: footnotes fixed. Sorry.