CD collection is getting stale........

Check out Agalloch's The Mantle and Pale Folklore. Its great folk and ambient stuff.

Let's not forget Ashes Against The Grain!
Since you're into Opeth, I'll make you some recs:
Ikuinen Kaamos - The Forlorn. Great, melodic, melancholic, progressive and beautiful death/black from Finland. Quite like Opeth, except a little more black metal.

Ne Obliviscaris - The Aurora Veil. Single best demo in the entire existence of the universe. No genre can do justice to these guys, but at a pinch, you could say progressive black metal with a violin. Except it's a million times better than that makes it sound. Much the same with Ikuinen Kaamos.

Trivium - Ascendency. Revolutionized modern metal. Just joking, lulz, but get the other two above albums! And Agalloch's 'Ashes Against The Grain'!
 
well if you like a bit of stoner Monster Magnet, or if you like the something really different The Enid
 
if the guy has as much cd's as he claims he does, then he'll probably know almost everything that has been mentioned here ... come on, recommending Tool??? who doesn't know 'em???
 
try some "callisto" (if you don't mind them being a christian band), pretty amazing postcore shit!
if you want some cool shit try some orange goblin, they're pretty sweet.
 
The album Believe by Disturbed. It's a bit lighter than the heavy stuff recommended here and heavier than the light stuff on here, and overall it works out amazingly. Guitar that doesn't suck, same with drums and the rest of the music, coupled with actual good lyrics sung by a good singer. Great album.
 
The album Believe by Disturbed. It's a bit lighter than the heavy stuff recommended here and heavier than the light stuff on here, and overall it works out amazingly. Guitar that doesn't suck, same with drums and the rest of the music, coupled with actual good lyrics sung by a good singer. Great album.

I disagree, it would be a waste of time to get this album.
 
I would like to recommend IN MOURNINGs Shrouded Divine, the Opeth-influences may be a tad too obvious ;) but it's a great album.
http://www.myspace.com/in_mourning

shrouded_divine.jpg
 
I'll give ya some suggestions

Leonard Cohen - Songs of Leonard Cohen (folk)
Simon & Garfunkel - The Greatest Hits (folk rock)
Bob Dylan - Best of Vol1 & 2 (folk/rock'n'roll)
Joni Mitchell - Court & Spark (jazzy folk??)
Pj Harvey - Stories form the City, Stories from the Sea (alt rock)

Mew - All albums (alt rock)
Grizzly Bear - Yellow House (Psychedelic rock/pop)

Harmonium - Cinquieme Saison & L'Heptade (folk prog)

Also, try some jazz-influnct stuff like Steely Dan, Talk Talk, David Sylvian...

I think it's enough, i won't overload with you with a thousand recs.