Hmm... I'm trying to think of my favorite apps, and well, I'm drawing a blank.
I know for a long while I had a bunch of networking applications on my Evo, but a lot of those require root, and are only good to have if you're into networking.
Some other apps that I've enjoyed are:
> ES File Explorer
> TweetDeck/TweakDeck (I used to use tweetdeck, now I use tweakdeck)
> Wifi Analyzer
I also had all the old Tiger GBC/GBA NES/SNES emulators on there, but the site's down lately