Animation Shop
You need to do animation on the web? One of the best and least expensive products for creating animation is called Animation Shop. It comes bundled with Paint Shop Pro and integrates with that product (Paint Shop Pro lets you edit each frame and Animation Shop puts the frames together).
My wife swears by this program. She loves it and uses it almost daily to create beautiful GIF animations. I've found it far easier to learn than other similar tools, and the price is right as well.
How does it work? You begin by editing your frames in Paint Shop Pro. Now, since Paint Shop Pro has full layering capability, you can move things around as needed. Once you finish a frame, you export it to Animation Shop and place it exactly as you want.
For example, suppose you wanted a spinning wheel? You would create the first graphic of the wheel in Paint Shop Pro in two layers. The first layer is the fixed portion and the second is the spinning portion. Export to Animation Shop as frame one. Now, rotate the spinning layer a few degrees, then export as frame two. Do the same for frame three and so on. Now go into Animation Shop and set the duration of the frames and save the image.