Perhaps I'll fix up my lame icon to use this new one, otherwise you'll just have to make do with: buzz.icn. I didn't even make a nice mask, sorry.
To get this to show up for your app just replace applet.icns in Contents/Resources under your "Google Buzz.app" directory (You might need to click show bundle contents or something). Make sure you call it applet.icns. Finder is slow about updating icons, so you can quit it from activity monitor if you're impatient.
I used Icon Composer which I guess is part of XCode under /Developer/Applications/Utilities.