I currently have the Nitto Invos:
http://www.nittotire.com/#index%2Etire%2Einvo

Next I think I'll try the Vredenstein's:
http://www.vredesteintire.com/products/SESSA.asp

I've also heard good things about the Kuhmo Ecsta SPT's if you can use a thre season tire.

I think all three of these are excellent, and the prices are all fairly friendly.