Michael Coleman has some Paint shortcuts we might have forgotten to tell you about.
AE LiveDocs Help has the other shortcuts for CS3 and CS4, and of course covers Paint tools: Brush, Clone Stamp, and Erase. The current basics of paint in AE is discussed at Lynda.com in After Effects CS4 Essential Training; it may become free at some point on AdobeTV but now the CS3 training for AE Paint is free on the Adobe Video Workshop.
Update: For Photoshop, John Nack has Layer-related shortcuts you might want to know, and Scott Kelby hosts It’s “Guest Blog Wednesday” featuring Bryan Hughes! to remind you of the useful features in PS CS3 and CS4.