I've got a near new pair of panaracer ribmo's laying around. 26x1.75. semi slick/Light tread. PM me if you are interested.

As said before, just use spacers and a single cog. Surly makes a singlespeed kit as do a few others. You may need a chain tensioner if you don't find the perfect gear ratio.

Heres a good place to start:
http://www.mtbr.com/ssfaqcrx.aspx