Among my list of the top domains names I used to own and wish I hadn't let lapse is annotator.com. I actually had a site up on it at one time that offered a way pre-Third Voice, web-based tool that let you put little "sticky notes" on any page on the web. Granted, it was also way alpha. But...damn. I was reminded of this via Edd Dumbill's rant about Annotate.net on his new WriteTheWeb site (which is very interesting, btw -- check it out).