So here's one (temporary link, will eventually remove if used or not), made from the logo. 64 x 64 (decided on that size after seeing that Google+'s uses those dimensions), 8 bpp, 1-bit alpha (transparency to the sides of the box since logo doesn't scale directly to a square), 256-slot palette. Testing it on a server it works fine using the latest versions of Google Chrome, Mozilla SeaMonkey, and Opera...