Sorted by how much it will suit your needs.
Bush - Letting the Cables Sleep (This is ****ing beauty, get it now)
Bush - Bonedriven (****ing beauty)
The Vines - Mary Jane (This is beauty..)
Course Of Nature - 1000 Times
Placebo - The Crawl
Placebo - Summer's Gone
Course Of Nature - Caught In The Sun
The Vines - Autumn Shade
Bush - Straight No Chaser (see above)
Radiohead - Fake Plastic Trees
Weezer - Death and Destruction
Placebo - Burger Queen
Radiohead - Let Down
Bush - Inflatable
Incubus - I Miss You
Weezer - Only In Dreams
Bush - Out Of This World (about death)
The Buzzhorn - Pinned to the Ground
Placebo - Narcoleptic
Audioslave - Shadow On The Sun
Limp Bizkit - Behind Blue Eyes
Linkin Park - My December / My Dsmbr
Weezer - Undone, The Sweater Song
Staind - Outside
Placebo - Ask For Answers
Radiohead - The Tourist
Radiohead - Sail To The Moon
Placebo - Centrefolds
Bush - Alien
Audioslave - I Am The Highway
Bush - Glycerine
Radiohead - (The Album OK Computer)
Incubus - (The Album Morning View)
Portishead - Most of their songs
The Buzzhorn - Holy Man
Lostprophets - Last Train Home (not slow, party hard)
Lostprophets - Last Summer
Bush - Dead Meat (Slow, then hard)
Puddle Of Mudd - Blurry (not exactly slow)
Daft Punk - Digital Love (not Rock)
Enjoy. Some of these songs easily get me to cry, but that's just me. I'm not kidding. Note that some of these contain violins, pianos, contrabass and more orchestral stuff so yes, this is a good compilation.
It would be nice if someone could just quote this so he actually gets to read it.