I'm in love with the Challenge Parigi-Roubaix clinchers, which are made from the same casing and tread as the tubular version. I'd try the tub version immediately if some nice tubular wheels came my way. If you want fat tires and are willing to spend a premium tire price, I recommend them highly.

If you want cheap tires, there's none cheaper than Andy Muzi's 3-for-US$50 tires. Some folks really love 'em: http://www.yellowjersey.org/tt.html