I use Vittoria Evo CX, 21mm. Fast, smooth, round. I like these best for their consistency and predictability. Run them at about 120-130 psi.

I also have Conti Sprinters - lumpy, not as straight. Relegated to secondary wheels or as spares or, eventually, for some training tubulars (for whatever reason). Run these at 160-170 psi since they feel flat at 120 or so.

I'm going to be trying Bontrager's tubulars ($89 and $79 on their site). Made in same place as Vittorias, figure they'll be reasonably good. Bought them, have not even stretched them. Sitting in a pile in my basement.

cdr