The most popular XC tire is the Panaracer Firee XC Pro ( Ithink it's pro)

They weren't in the top 10 of the Mountain Bike Action Tire report-
but it is the readers most popular tire.

Apparently it's good in a variety of conditions- but especially hardpack.

You can usually get them pretty well anywhere- if the ads in the cycling mags are to be believed.

Check Ebay too.

Kimba