Opera Mini – Fast alternative browser to Safari, like the UI and Start Page (Free)
Yak – Free single or group chat application using mobile internet connection (Free)
Fring – VOIP service similar to Skype except you can use your 3G connection instead of wifi, also incorporates twitter, msn messenger and a few others. (Free)
Self Photo – Great Camera function for camwhoring especially if you have fat fingers and cannot quite press the small camera button without shaking massively. This one allows you to press any where on the screen. (Free)
Draw It – Good for doodling, you can save a copy in your photos folder when done. (Free)
SimpleMindx – Great for mind mapping (Free)
Dropbox – drag and drop saving of files from your PC and accessing them via your phone. Also easy sharing via email link (Free)
TwitBird – Twitter app for twittering (Free) option to upgrade thought not necessary for most.