Kreitlers are the gold standard, and are priced accordingly.

I have the aluminum rollers made by these guys:

http://www.sportcrafters.com/welcometop.htm

I have had absolutely no problem with these, so you should consider them as well. I bought mine from Nashbar, but they don't sell them anymore. The owner is very responsive re how the resistance unit works, so I'm sure he'd answer any additional questions you might have.