Two manufacturers that I can think of at the moment who offer very good deals on Ti frames are Douglas and Lynsky. This is for new Ti frames, btw.

Of course, when considering the retail cost of a Colnago steel frame, Bianchi, or any other big name brand might be nearly twice as much as a Lynskey frame; if you want Ti, it's a no-brainer.

In fact, because of carbon's popularity in the pro peloton and fast club rides (plus it's cheap to produce on a mass scale), and the currently popularity steel has enjoyed with many big manufacturers, Ti has been sort of forgotten, which is why it can be obtained for a steal (pun intended).

As a point, on CL in the last couple months, I've seen three Ti Schwinn Paramount for less than $600; one was an entire bike with Dura Ace, IIRC.