First you have, of course, Photos, followed by Notes. The ability to tag people in both is great. I love that I can see photos of me and my friends beyond just the ones I take. Brilliant! Events, too, is a huge part of life now. If you want to know what's happening, where do you go? Facebook Events, of course (I also use Yelp when I'm in cities to find food-related public events).
My favorite games are Bejeweled Blitz, Mafia Wars, Dolphin Olympics, Word Challenge, and Geo Challenge. I also enjoy keeping track of Where I've Been with that application. I've found a downloadable photo uploader which is much more functional than the one in browser for Facebook.
Now go forth and play some flash games! Instead of researching for a 20-page paper. Yes, that's the spirit!