I use these and love them.

http://www.sportcrafters.com/

Solid 3.5 inch rollers provide enough resistance without adding parts. They are well made in the US and cost a lot less than Kreitlers. There's lots of information on the their website and they are responsive to emailed questions. I bought the aluminum ones as I plan on carting them to races. Rumor has it that PVC rollers will warp in the sun.