At the moment for me it is http://www.fastwebhosts.us which I am willing to sell for the right offer. It isn't even a year old yet and I didn't promote it much. But it could be a great website, it comes included with the script.
It's one on birding that a friend of mine and I created in 2000. At the time he had been producing a manual for bird watching which he circulated during birding outings, completely funded from his own pocket. I then thought it could be cool to put it up on the Web. Great learning curve. Content has changed completely since then, but it's still chugging along great.
My one and only domain was opened up 2 years ago and has since hosted several totally different web sites. I find it best if you retain a small number of domains and build and adapt atop of them rather than hosting several and forgetting about many of them.