For standard dropouts, Surley makes the "singulator", which is a pretty good (and simple) tensioner. Its also cheaper than a track frame

If you have an existing set of wheels that take a cassette, you can either make or buy spacers to get the chainline right. If your wheels take a freewheel, look into 16-tooth BMX freewheels.

Spot makes some very good stuff, or so I hear- I'm trying to do my ss project on a budget!

A VERY good site is http://www.singlespeed.cc
Good info, and a HUGE links page!