I have an old rear wheel that gets suited up with an old tire that's no longer road-worthy and a spare cassette. I have an endless supply of junk tires, so I just chew through those during the winter. To me, a second rear wheel is worth the expense to not have to change tires every other day or trash a nice tire on the trainer.
DH, on the other hand, has to use that cheez-yellow trainer-specific tire by Continental. He seems to generate enough force and heat that he trashes ordinary tires and they make horrible squealing noises when used on the trainer. The Conty is nice and quiet by comparison. Be forewarned- that tire is very very hard and a major PITA to mount. You'll want to leave that one on a spare rear wheel...
I'm currently using Vittoria Diamantes ($$$, but so nice!) on one bike, and Conty Ultra Races on the other. I didn't think I'd like Ultra Races, but they've been good. I might consider buying them again- they're only ~$35 each.