I thought truck balls would be good too, but they are too expensive. Note: the website I checked had the white balls as "flesh" colored. It turns out the manufacturers of BumperNuts aren't very "progressive."
I have access to a copy of the Unzipped with Beau on the cover. It is signed "Happy Birthday Adam" You can forge an "s" on to it and make for ulta-LULZ.
What about those dayglo plastic things you put on your bike spokes that slide up and down as you ride and make neat clicky noises. Do they still make those?
http://www.bumpernuts.com/Order%20Page.htm
You don't have to factor shipping into the $25, right?
$14.99
http://cockbibcrazy.com/happybirthdayblk.a…
Something personalized from Sausage-Stuffer.com?