Here's few apps that I use:
1) BeyondPod: a good app for getting podcasts. I'm using the free version, but the full version has a lot of neat features, as well.
2) gReader: Another RSS app. Not as pretty as Pulse or Taptu, but I've found it to be faster and a little less laggy. YMMV
3) QuickPic: An alternate gallery app. Definitely prefer it over stock
4) Dropbox: Fairly well known by now, but I find it extremely useful for cloud file storage
5) AudioManager Pro: Great app for controlling volume. Also allows for profiles on a schedule, so you can have the phone automatically turn down ringer and alert volume at night.
I like to change up my device's look a lot, so Minimalistic Text, mClock, Desktop Visualizer and WidgetLocker (all of which have been mentioned) are all useful.
As far as games: Cut the Rope, Fruit Ninja, Wordfeud, psx4droid (PSX emulator), and WordzUp! (a Boggle-like game) are the main ones, though now that I'm off the OG, I'm starting to try out some of the more intensive games.