GIFmaker is free and does this. Should be on download.com. It's old though. It runs in classic I think. I do not know about an X solution, as its been awhile since I've done any graphics that I needed to animate.
Check versiontracker.com -- I'm SURE they'll have at least one option for you.
I'm with mac-lad on this one. For 2D GIF animations, nothing tops the quality of Adobe ImageReady (comes with Photoshop). If you want something truly interactive, you may have to work with Flash MX. Using either program will require some getting used to.
Of course, if you don't have Photoshop, you'll have to borrow a freebie, or one of the many shareware props.