All my favorite sites have been mentioned already but.. I would like to add that Google offers an internet library. When you click on the "Books" feature in the options (same line as Images, Videos, etc), then click on 21th, 20th or 19th century, Preview and full view, you can find some interesting book that offer partial or full view of their contents, and you can learn some good tips or techniques.
I thought it was very useful for trying the strips and curves.
Good luck with your presentation tomorrow!