+1 for Advanced Task Killer – can help you “kill” selected apps running in the background that are taking up memory, battery power etc.
Quick Settings – really useful app for switching WiFi, mobile data, GPS, bluetooth etc on and off. I really like the auto brightness setting on this.
Aloqa or AroundMe – see what banks, restaraunts, cash machines, pubs, garages are near.
Net Counter or 3G watchdog – so you can keep an eye on your data usage.
AK notepad – for when you haven’t got a pen.
Songbird remote – Rip your music collection to pc and contro it all from anywhere in the room.
Robo Defence – Tower defence (is that what you call it?) game.
Goggles – take a picture of something (book, bike, car etc) and it’ll identify it and direct you to the web giving you info on it.
Loads more on there – just have a search and download, they’re mostly free and you can always uninstall if you don’t use em.