It's easier to show the apps that I have, and explain below..
(Yes I have them sorted alphabetically
)
Band - Play some instruments
BBC iPlayer (web app) - Watch BBC programmes on demand
iBomber - Good little top-down bombing game
ChaseTheDot - Reflex testing, good timewaster
Converter - Useful converting app, also does accurate currency conversions
Decibel - Sound Level Meter, pretty accurate too!
Deliveries - Delivery Tracking App, extremely useful
Digg (web app) - Handy for checking out news, good UI
eBay - Self explanatory.. more of quick-check than an auction manager though
Engadget (web app) - Nice way to check up on tech-specific news
Facebook - For socialising and posting nekked pics
Flight Control - Very entertaining air-traffic control game
Flixster - Movie times and reviews (has Facebook integration)
iFooty - Checking tables and upcoming fixtures / results
Invaders - Classic arcade game of Space Invaders
Jelly Car - Easy to learn, hard to master platformer
Last.FM - Discovering artists & useful when radio sucks
Mac Rumors (web app) - Check up to date with latest Mac news
Monkey Ball - Sega platformer
Pac - Man - Needs no introduction!
Remote - Control iTunes / Apple TV
Shazam - The pub's worst "guess that tune" nightmare
Skype - Make free calls on Wi-Fi
Sonic 1 - Another childhood classic from Sega
Speed Test - Useful for checking web / mobile speeds
Stanley Level - Novelty spirit level app, useful
Tetris - Highly addictive classic with some good new game modes
Trism - Fiendishly difficult be-jewelled-like puzzle game
TV Plus - Used to remote-record Sky HD box / check TV guide
TwitterFon - Sharing pointless info with the world via Twitter
Wiki Mobile - When you need a wikipedia injection
X-Plane - Great flight sim. Good level of detail too.