If a domain is not available you can try using action words, 37signals style, like basecamphq.com and campfirenow.com

You could try some domain hacks, but some people don't like them. DO try to get the similar .com of it, for a conversationally link drop.

You could always create some wierd name, like weeeezo or something new and hip like that, but some people might just get confused or not like it all.