Substrate Live Wallpapers one of the best things about nexus one is the live wallpapers. this set of wallpapers is like having art being made in front of your eyes, just for you.
MixZing Upgrader The Nexus One has an expandable capacity of 32GB, making it one hunk o' music playin' awesomeness. This app has 3 widgets to use on your screens, and helps you create playlists based on similar music.
Google Translate The Voice functionality on nexus one is perfect for this app. speak a sentence into the app, and you'll get a translation in a bunch of different languages! you can even save a few handy phrases for future use.
Google Goggles The Flash on the Nexus one (thank goodness) along with this tool will help you figure out what that bottle of wine is all about just by taking a photo. it also allows you to snap logos, contact info, books or landmarks and get more info!
App Referrer Assuming you already have the Barcode Scanner app, this is a great app to spread the joy of your most favorite apps!