The album was Back on the Road: - 32 Tracks of the Very Best Of Progressive Underground, and many of the missing tracks I've picked up on iTMS. Here's the listing:

Disc 1

1. All Right Now by Free
2. All Along The Watchtower by Jimi Hendrix
3. Living In The Past by Jethro Tull
4. Hocus Pocus by Focus
5. Eight Miles High by The Byrds
6. Rainbow Chaser by Nirvana
7. America / 2nd Amendment by Nice
8. Northern Sky by Nick Drake
9. On The Road Again by Canned Heat
10. Paranoid by Black Sabbath
11. White Rabbit by Jefferson Airplane
12. Mona by Quicksilver Messenger Service
13. My White Bicycle by Tomorrow
14. Love Really Changed Me by Spooky Tooth
15. Race With The Devil by Gun
16. 10.30 Returns To The Bedroom by Soft Machine

Disc 2

1. Strange Brew by Cream
2. Silver Machine by Hawkwind
3. Meet on the Ledge by Fairport Convention
4. Fire by The Crazy World Of Arthur Brown
5. Woodstock by Matthews Southern Comfort
6. Paper Sun by Traffic
7. Do It by Pink Fairies
8. Tom Tiddler's Ground by Roy Harper
9. Black Night by Deep Purple
10. Out Demons Out by Edgar Broughton Band
11. Loves Like A Man by Ten Years After
12. Venus In Furs by Velvet Underground
13. Fresh Garbage by Spirit
14. One And One Is One by Medicine Head
15. Change Song by Blodwyn Pig
16. Something In The Air by Thunderclap Newman

The bold tracks are the ones I currently have - 24 out of 32, and most of the ones I really wanted. Anyone got a source for the others? In particular, I wouldn't mind:

• Living in the Past (update: I've now got this, thanks to Dave Fitch. As soon as Apple see fit to add some Tull to iTMS, I'll shell out real cash for it). Now on iTMS and bought.
• Mona (it's on iTMS, but only if you buy the whole album)
• Woodstock (no, I do not want the Joni Mitchell version!) Now on iTMS
• Tom Tiddler's Ground
• Black Night (I have the Vic Reeves synth rock version somewhere) Now on iTMS

Meantime, for your listening pleasure, here's the iTMS Back on the Road iMix

(Incidentally, apropos of nothing in particular, we watched School of Rock the other night and found it much better than I'd expected)