Lip-syncing

This link is mainly for 3D:
http://www.comet-cartoons.com/toons/3ddocs/lipsync/lipsync.html

For 2D you can work up a set of eight to ten mouth shapes as your starting point. Then you must analyze your dialogue track for phoneme (sound) and viseme (matching graphics) placement. Magpie is a software you can get for not much that does this well. Another similar but free program is JLipSynch.

A lot of it depends on your method of animation.

A good thing to know is what program you are using. If you are using Flash, I just finished writing a tutorial on it yesterday. All the information is there, even if the navigation isn't done yet. Here is the link:

http://www.cartoonsolutions.com/clubhouse/mouth_comps.html

Here is another one I just finished. This one focuses on using an x sheet in flash to help the lip sync process.

http://www.cartoonsolutions.com/clubhouse/lip_sync.html