Whatdeliversto.me and whatdeliverstome.com -- both intended to compete with GrubHub, but never happened.
Typemotion.com -- was a blogging platform that was actually pretty good. Got acquired for a small sum of money, then the buyers folded and gave the domain back. It's an odd story, but I've always liked the domain.
Governaut.com -- was a blog for awhile when I was a federal contractor. Had a site set up to act as a social network for other federal contractors and discuss common IT situations, work constraints, etc. Never got around to doing more than just the blog though, and never got traction.
Vaginawear.com -- bought while I was drunk. I remember there was a really good idea behind it, but that idea was nowhere to be found after I sobered up.
AppDiem.com -- Groupon for mobile apps. We were partnering with mobile developers to release on-sale apps, a new one each day for each target platform. Shuttered a year a more ago.
babylum.com -- Was designed to be just like leandomainsearch, as a side project. Then leandomainsearch launched,a nd babylum was no longer needed.
Then, there's the 'porn' domains. This was another drunk idea that I realized I didn't have the gumption to actually do when I was sober, and since I couldn't be expected to be drunk through the entire development process, eventually just realized that I'd not do anything with it. These domains are gold though (in a porny sort of way.) - getnakedgetmoney.com, getnakedgetpaid.com, getnakedwinmoney.com -- I think the domains explain the business models.