While I agree with most users that posted before, it all come down to your usage and preference, this are in my opinion all the "absolutely" any jailbroken phone should have.
SBSettings - quick access to all your settings - can't live without it

5 Icon Dock - name says it all, not sure why we can't have 5 icon from stock
iFile - File Manager
Backgrounder - real multitasks, if you "need" some app to be running at all time that is still not allow to multitask
LockInfo
BiteSMS - Way better SMS app, countless additional features, quick reply, quick compose, and more.
Now Cool to have:
3G unrestrictor (paid - $2,99) - Allow to use 3G for WIFI only app (once its update it will allow FaceTime over 3G
MyWi (paid - $19.99) - 3G hotspot Tethering