If your driving on I-15 through Utah, check out these record stores:
Randy's Records
157 East 9th South Salt Lake City, UT 84111
A lot of vinyl, and in most genres. This dude's been around a long time.
Graywhale
208 South 1300 East Salt Lake City
They've got a great selection of new and used CDs, the vinyl section isn't as extensive as Randy's, but there are some great gems for the taking.
The Heavy Metal Shop
63 Exchange Place Salt Lake City, UT 84111
A great store, but small. Metal is the main draw. There is another record store around the corner that has a bit of old used vinyl. I think its called uprock records.
Raunch Records
1119 East 2100 South Salt Lake City, Ut
The punk/thrash/metal/whatever hot spot. Raunch has vinyl, cds, and tapes. All your skate punk favs. Even some skateboard stuff too.
Groovacious
173 North 100 West Cedar City, UT
This place has vinyl, cds, tapes, even a few 8 tracks. A wide range of genres, and a lot of cool surprises.
Get ready to spend some money, and have fun on your trip.