There are thousands of web hosting / co-location services out there, but as far as I know, there are none that will co-locate a server that can be shipped in a shoebox, and will treat it like it belongs in a rack, next to the big boys.

Macminicolo.net does just that.  You send them a Mac Mini (or buy one from them at the going rate) and they will hook it up to a smoking fast connection in a managed facility.  You get full access to your machine, and can even (optionally) manage the power supply remotely.

Worried a Mac Mini would not be able to keep up with your needs?  You’d be surprised.  They perform very well under load, especially maxed out with RAM.  In addition to being able to host unlimited domains yourself, it’s a great way to keep remote secure backups, manage an SVN repository, or just to use as a personal file server.

I’ve been using their service for about a year, and I’m extremely satisfied.