Travis
Screaming Trees
Mad Season
Thanos for all the suggestions, but I am <B>really</B> not interested in audio books. I’ve already driven 1,200 miles two ways in the past, and music served me just fine.
Keep the song suggestions coming though please 
I’ll be doing a 500-mile roadtrip myself in the next couple weeks. I’ve got Sirius satellite radio, and when I get tired of my usual music streams and the comedy channels, I’ve got these CDs:
Pink Floyd - The Wall (for some reason this is my hands-down favorite for road trips)
Bruce Springsteen - Born in the USA and The Rising
The Eagles - Hotel California and One of These Nights
Eric Clapton - Unplugged (if I can pry it out of DH’s hands)
Tom Waits - Heart of Saturday Night
Mark Knopfler - Sailing to Philadelphia
Ian Hunter - You’re Never Alone with a Schizophrenic
J. Geils - Freeze Frame
I’ve also just ordered up Ta-Dah by the Scissor Sisters - someone just turned me on to them and I think this will make an excellent road trip CD.
Wow. Where to start? 
For a Pink Floyd suggestion, I’d go with ‘Wish You Were Here’
My next suggestions are mostly a little bit out of your type of music, but not so much that you wouldn’t enjoy them. They all rock.
Talking Heads - Remain In Light
Rolling Stones - Exile On Main Street
Hepcat - Right On Time
Psychedelic Furs - All Of This And Nothing
John Hiatt - Hiatt Comes Alive At Budokan?
Dave Davies - Live at Rock Bottom
Moved from IMHO to CS.
Given you seem to learn more towards the harder, guitar-driven end of the music spectrum, I would recommend:
Lynyrd Skynyrd - Gold and Platinum.
The Black Crowes - Shake your Money Maker
Molly Hatchet - Flirtin’ With Disaster - Great road album
BuckCherry - 15 This is what happens when you cross Guns N’ Roses with Aerosmith.
Stevie Ray Vaughan - You must have some Stevie Ray. Get his greatest hits album. Best.Guitarist.Ever.
The White Stripes - Elephant, White Blood Cells, and De Stijl are must-have CD’s for anyone who likes rock music.
If you like Guns N’ Roses, you might want to check out *Velvet Revolver, which is basically Guns and Roses with Scott Weiland replacing Axl.
You seem like you like the Classic Rock as well, so I’d suggest some early Clapton or Cream in there.
The soundtrack for Fear & Loathing in Las Vegas is pretty fine road music. A truly eclectic selection of tunes plus snippets of dialog.
Watch out for the bats!
Dire StraitsBrothers in arms and Making Movies
MarillionMisplaced Childhood and Clutching at Straws
sample of Misplaced Childhood
Kraftwerk- Autobahn
Queen. Get thee some Queen.
And an audiobook. Preferably something fast paced, like a thriller.
Sorry I didn’t see this sooner, hope I’m not too late.
For more Pink Floyd; I like Animals and Wish You Were Here, but not having Dark Side of the Moon is like being a fan of Nirvana and never hearing Nevermind.
If you like Rush for the drumming, I’ll recommend Dream Theater (I esp. like Images and Words). Mike Portnoy is one of the few drummers alive in the same class as Peart.
From your list I think you’d be a fan of Gov’t Mule. (There newest, High and Mighty hasn’t left my car CD player in two weeks).
Every road trip has to have a copy of the Allman Brothers At Fillmore East and the better road trips have a copy of Little Feats’ Waiting For Columbus.
I don’t usually go anywhere without some Santana. If you like Pink Floyd, you’ll probably get into Caravanserai. (Absolutely nothing like what he’s been doing lately, I’m just sayin’)
If you just want to groove along, ignore the rest of this. If you want to use this as an opportunity to really listen to some music, I’d suggest some or all of the following bands (and the Derek Trucks Band):
(old school prog-rock bands that are not Kansas)
Yes
Emerson, Lake and Palmer
King Crimson
(jambands that aren’t Phish or Dave Matthews Band)
moe.
Widespread Panic
String Cheese Incident
(neo-prog bands that aren’t Spocks Beard)
Flower Kings
Transatlantic
IQ
Commander Cody Truck Songs
Asleep at The Wheel
Little Feat - Feets Don’t Fail Me Now
<slight hijack> If you’re going to drop this much coin on music, maybe consider a satellite radio setup. Both XM and Sirius have most any type of music you could possibly want, with some good talk programming too. I have one and I absolutely love it. </slight hijack>