Are there any companies that are particularly good? What do you recommend?

I can search ebay, but only once I know what is a good bike.

I do want a light, efficient singlespeed: price is not the only factor. I already have an old mountain bike on hand which I'm using for spare parts. I can use the steel frame to create an inexpensive singlespeed, but then it would be a singlespeed with a heavy, clunky mountain bike frame with massive shocks. What I really want is something small and efficient.

I would like this to be my primary bike for transportation; something I really enjoy riding and can continue to enjoy for years to come.

Anybody have a favorite singlespeed or have an online supplier that they recommend for its quality versus the price?