It depends on what you want to do with the phone when it comes to choosing the applications.
I use the flicker app, Twitterific for tweets, Skype for when I'm connected to a wireless network, Alarm Clock, eBay, IMDB, yell, amazon, the national trust, the telegraph and the list goes on and on. I also have a pile of apps installed for work that allow me to monitor and access servers if needed.