Bookmark this site. Everyone needs this at his/her fingertips. Everyone also needs to be active in this organization, if you ask me.

Marijuana Law Reform - NORML

You can read more about potential penalties in the site's Legal Issues area, which deals with U.S. laws on a state-by-state basis:
State By State Laws - NORML

The Image Reaper is correct. If you're already in legal trouble, get an attorney with experience in dealing with cannabis/cannabis defense. The NORML site is a good place to start.