Depends on what you want i guess. Things which make some sense - free and not free - Cydia and otherwise would be:
MyWi - wireless tethering
Google Maps - you should know this
GoodReader - open various formats including pdf
MyDataUsage - monitor data usage
DropBox - you should know this
DeviceStats - handy tool. Shows memory and running processes and such.
Skype - you should know this
MakeTones - make ringtons from any audio on device
SbSetrings - handy tool. Reset springboard, enable/disable stuff quickly.
MxTube - watch / save YouTube videos
TeamViewer - you should know this
AirBlue Sharing - send / receive files using bluetooth. Something Apple forgot.
If it not in the app store then it in Cydia. Have fun