In order of importance to me:
iRealQuickSMS
Backgrounder
SBSettings
5 icon dock w/ Dock Flow
Categories
Safari Download Plugin
iFile
Winterboard
xGPS
dTunes
CyDelete
AptBackup(haven't had to use yet)
I used to have StatusNotifier and pretty heavily modded themes, but I noticed such a huge battery drain that I had to remove them. I now am experiencing excellent battery life so I'm pretty content!