I'm using RedLaser for barcode scanning, CameraZoomFX as a replacement for the native app, Beautiful Widgets, avast antivirus, Dolphin browser, Dropbox, File Expert, Google Sky Map (which pointed to the sky will tells you about the constellations), MoboPlayer, Pano (to make panoramas with the camera), Pulse for news, Superuser, Titanium Backup, AdFree, and an awesome guitar tuner with an inappropriate name.
I want to try out these soon:
SpeechTransPro (which can take foreign speech and translate it)
Viber (free calls to any country)
Wifi File Explorer
Root Explorer
Lapse-it (time lapse photography)
Also app called Clik that may one day allow you to wirelessly use your smartphone on your TV.