If you want a vintage Single Speed go on CraigsList and look for your local bike flipper. Single Speed is a big market...there are flippers catering to you.
If you're gonna go modern, I love my Raleigh One-Way for its versatile frame with lots of braze ons and attachment points. (plus it rides nice)....If I ever get bored of having it as a single speed I can easily convert it to something else.