I would Install.
- Dolphin Browser (Better internet browser)
- GoSMS (Better Text message app)
- eBay
- Tweetdeck (Twitter/Facebook app)
- Speedtest (Test Wi-Fi or 3G Speed)
- 3G Watchdog (Keep track of 3G usage)
- Quickpic (MUCH Better Gallery)
- Lookout (Security and tracker if u loose the phone)
- Barcode scanner (Useful)
- MoboPlayer (Better video player)
- Angry Birds (Awesome game)
- Dropbox (If you use Dropbox)
- AK Notepad (Good notes app)
- BBC iPlayer
- Glow Hockey (Good game)
- DroidStats (Tells u how much mins/txts/web u have left)
- Google Earth
- Google Goggles (Search web with pictures)
- Phandroid (This forum on your phone

)
- SoundHound (Find the name of a song thats playing)
There are just a few really good ones

Enjoy!
