Update - 3-27-08: I've had a lot of people asking me if it's OK for them to do *insert particular thing here* with my art. So, I'm going to try to create an all-inclusive list here of what's OK, but don't hold me to it :) More things than this are probably fine, I just don't know about them yet!
Creating: Sig Tags, with or without names or slogans - Stationery for Emails - Websets, as long are they aren't for sale in any way, or used on a commercial site-
Tutorials, again, not-for-sale - Avatars (Those little icons in chat rooms)- Tubes - Animations (I ask that my character's faces aren't covered during the cycle)
Framing (Adding a digital frame to an image) - Game mods (Like Sims, where you can add art to your houses, etc)
Tags, etc. may be made as prizes for groups that have online competitions (I've seen things like "Best lion tag of the month, or such), but
please let me know that's what it's being used for in advance!

You May Not: Sell ANYTHING you've created with my art. That's my job, and I hate being hungry.
Print anything you've made with my art (or my art in any way at all - even unaltered)
Add or imply any kind of derogatory, racist, hate, sexist, vulgar or otherwise inappropriate message to my work
(I reserve the right to decide what is inappropriate, much like the FCC.
But if it's funny enough, I may allow a certain amount of "Vulgarity" as they would phrase it, so if you must, you have to send it to me for approval first.)
If you use more than one artists' work in a creation, they must ALL be creditied. If you use a photo, the photographer MUST be credited.
If you took the picture, then give yourself a credit for it visibly! If you think it's 'Public Domain', it probably ISN'T!
I don't want to see any more tags, etc. with obviously uncredited additional elements. That's the kind of thing that
the U.S. Congress is using to justify their "Orphan Act" in the first place. Let's not help them ruin our fun!