Depending on how adventurous you are, My Tracks by the Google team is great. It will use your GPS and track your path giving you a ton of stats like speed, distance, elevation, time, etc., and will give you the option to export it to Google Docs. I do a lot of running so this was nice for tracking my runs, but it also came in handy for finding the shortest commutes to work.
When I was on BB, I used to use "Poynt" quite a lot. I now use "Google Places" exclusively.
Another Google app I love is "Google Translate" comes in very handy!
Buzz ties into gmail because it will use your contacts with gmail, and such. Go on gmail with your computer and find the buzz label, should be write under "inbox"