iMovie Training
iMovie Help
BGSU iMovie Tutorial - A nice PDF containing a description of all the buttons and functions that you can use for basic iMovie editing. Refer here if you are not sure what buttons do or forgot how to do something!
Mac Video Tutorial - Great website that shows you using video how to add effects and transitions to your video clips.
iMovie 10 Interface - If you need help with the new iMovie 10 interface.