I thought I'd throw together a quick list of good things to install from Cydia
5-Row QWERTY Keyboard - adds a new numbers row to your keyboard
BossPrefs - Advanced settings control
Categories - Create folders for apps
Clippy - Copy, paste hack
Extended Preferences - Adds more options to Settings
Five Icon Dock - Lets you have 5 icons docked instead of just 4
Flashlight - Flashlight app. Much brighter than the Apple app.
iMobileCinema - Safari app for flash videos
Installulous - Allows you to install downloaded IPAs(Apps)
KeepAwake - Keeps your wifi connection awake
MakeItMine - Allows you to change your carrier name
MxTube - Allows you to view and download youtube videos
OpenSSH - Allows you to SSH into your ipod or iphone
Safari Download Plug-in - Allows you to download things from Safari
SBSettings - Allows you to quickly toggle settings(Swipe the top banner to get to this)
Scrobble - Scrobbles your music to Last.fm
Search - Search through your email, sms, notes, and contacts
UserAgent Faker - Lets websites think you are using a real browser
John, whoever else has jailbroken, please add what you use and think is good to have.