The folks over in the Apache Jakarta project seem to do a decent job of naming their projects. Some of the better ones satisfy the sage advice that Sean & Adam have voiced above:

Alexandria
Ant
Avalon
Cactus
James
Jetspeed
Slide
Struts
Tomcat
Turbine
Velocity

It's interesting to note that tomcat.org takes you to a non-descript French site, while slide.org ends up at some kind of Spanish ecommerce site. The point being, the name was chosen on it's qualities as a brand, not on the basis of an available domain name. Besides, if people don't know the URL, they'll use Google. You just need to make sure the brand itself is easy to spell and remember.

To bad Alexandria is taken ...