As others ave said, check out sa-cd.net which lists just about every SACD title ever released. Many have reviews and links to various vendors where you can gauge at a quick glance the average price of that title. It's also worth checking out Quadraphonicquad.com for info and discussion on SACD and DVD-A releases.
The places I tend to buy from are Amazon, ebay, Burning Shed (for most Steven Wilson related music, whether as artist or mixer) and occasionally, CD Japan. Some OOP titles have crazy high price tags; I guess it's just a matter of how much you're wiling to pay for a particular title.
There's a dedicated thread on AV Forums (in the music section) dedicated to DVD-A and SACD chat where many members list their collection, which lets you know which releases are popular and perhaps worth getting if you like the music. I'm a relative latecomer, but so far have the following in my collection.
Blu-ray
Beck Sea Change
Derek and the Dominoes Layla and Other Assorted Love Songs
Dire Straits Alchemy (Live)
The Rolling Stones GRRR!
Supertramp Breakfast in America
Steven Wilson - Grace for Drowning
Steven Wilson The Raven That Refused to Sing (and other stories)
DVD-A (Includes some DD/ DTS releases)
The Alan Parsons Project - The Turn of A Friendly Card
Barclay James Harvest - Once Again
The Beatles - Love
George Benson - Breezin
Bjork - Debut
Bjork - Homogenic
Bjork - Post
Bjork - Selma Songs
Bjork - Vespertine
Les Brown Session #55
David Bowie Young Americans
LTJ Bukem Planet Earth
Caravan - In the Land of Grey and Pink
Nick Cave & The Bad Seeds - The Firstborn is Dead
Nick Cave & The Bad Seeds - Tender Prey
Nick Cave & The Bad Seeds - The Good Son
Nick Cave & The Bad Seeds - Murder Ballads
Nick Cave & The Bad Seeds - The Boatmans Call
Nick Cave & The Bad Seeds - No More Shall We Part
Nick Cave & The Bad Seeds - Nocturama
Nick Cave & The Bad Seeds - Abattoir Blues/ The Lyre of Orpheus
Nick Cave & The Bad Seeds - Dig, Lazarus, Dig!!!
Joe Cocker - Night Calls
Depeche Mode - Black Celebration
Depeche Mode - Violator
Depeche Mode - Songs of Faith and Devotion
Depeche Mode Exciter
Depeche Mode - Sounds of the Universe
The Doors - LA Woman
Emerson, Lake & Palmer - Emerson, Lake & Palmer
Emerson, Lake & Palmer - Tarkus
Donald Fagan Morph the Cat
The Flaming Lips - Yoshimi battles the Pink Robots
The Flaming Lips - At War With the Mystics
David Gilmour On an Island
Hawkwind Warrior on the Edge of Time
Don Henley The End of the Innocence
Insane Clown Posse The Wraith: Shangri-La
KD Lang - Invincible Summer
King Crimson - In the Court of King Crimson
King Crimson - In the Wake of Poseidon
King Crimson - Lizard
King Crimson - Islands
King Crimson Larks Tongues in Aspic
King Crimson - Starless and Bible Black
King Crimson - Red
King Crimson - Discipline
Lynyrd Skynyrd Southern Surroundings
Alanis Morissette Under Rug Swept
Motorhead - Overkill
No Man - Together Were Strangers
No Man - Schoolyard Ghosts
Nosound A Sense of Loss
Mike Oldfield - Tubular Bells
Mike Oldfield - Hergest Ridge
Mike Oldfield - Ommadawn
Glen Phillips Abulum
Pink Floyd - Dark Side of the Moon (4.1 Alan Parsons mix)
Porcupine Tree - Lightbulb Sun
Porcupine Tree - Stupid Dream
Porcupine Tree - Fear of a Blank Planet
Porcupine Tree - The Incident
Queen A Night at the Opera
REM - Out of Time
REM - Monster
REM - New Adventures in Hi-Fi
REM - Up
REM - Reveal
Steely Dan Everything Must Go
Sting Brand New Day
Talk Talk - Colour of Spring
Talk Talk - Spirit of Eden
Talking Heads - 77
Talking Heads More Songs About Buildings and Food
Talking Heads Fear of Music
Talking Heads Remain in Light
Talking Heads Speaking in Tongues
Talking Heads Little Creatures
Travis and Fripp - Follow
Jeff Trott Dig Up the Astroturf
XTC - Nonsuch
Steven Wilson Insurgentes
Wishbone Ash Bare Bones
Yes Close to the Edge
Neil Young On the Beach
Neil Young & Crazy Horse Greendale
SACD
The Allman Brothers Band Eat a Peach
America - America
Eric Bibb Rainbow People
Eric Bibb Spirit and the Blues
Bjork Medulla
Bon Jovi This Left Feels Right
Bottleneck John All Around Man
David Bowie - Ziggy Stardust
Can - Monster Movie
Can - Soundtracks
Can - Tago Mago
Can - Ege Bamyasi
Can - Future Days
Can - Soon Over Babaluma
Can - Landed
Can - Flow Motion
Can - Saw Delight
Can - Can
Can - Rite Time
Can - Unlimited Edition
Chicago V
Eric Clapton 461 Ocean Boulevard (SHM)
Eric Clapton 461 Ocean Boulevard
Eric Clapton - Slowhand
Miles Davis - Kind of Blue
Depeche Mode - A Broken Frame
Depeche Mode - Some Great Reward
Depeche Mode - Music for the Masses
Depeche Mode - Ultra
Depeche Mode - Playing the Angel
Dire Straits - Dire Straits (SHM)
Dire Straits Love Over Gold (SHM)
Dire Straits - Brothers in Arms
Nick Drake - A Treasury
Poor Boy Songs of Nick Drake
Bob Dylan The Freewheelin Bob Dylan
Bob Dylan - Bringing it All Back Home
Bob Dylan - Highway 61
Bob Dylan - Infidels
Eagles Hotel California
Donald Fagan - The Nightfly
Fleetwood Mac - Rumours
Foreigner - Foreigner
Marvin Gaye - Whats Going On (SHM)
Genesis - Trespass
Genesis - Foxtrot
Genesis - Selling England by the Pound
Genesis A Trick of the Tail
Genesis - Duke
Genesis - Abacab
Genesis We Cant Dance
Golden Earring Naked III
Goldfrapp Supernature
John Hiatt Master of Disaster
Billy Joel - The Stranger
Elton John - Honky Chateau
Elton John Goodbye Yellow Brick Road
Elton John - Captain Fantastic and the Brown Dirt Cowboy
Norah Jones - Come Away With Me
Sara K Play on Words
Sara K Hell or High Water
Sara K Made in the Shade
Carol Kidd - All My Tomorrows
Carol Kidd - Nice Work
Mark Knopfler - Shangri-La
Lynyrd Skynyrd - Second Helping (SHM)
Claire Martin Take My Heart
Claire Martin Perfect Alibi
Claire Martin Secret Love
Claire Martin He Never Mentioned Love
Claire Martin A Modern Art
Claire Martin Too Much in Love Too Care
Claire Martin When Lights Are Low
Claire Martin Witchcraft
Lavinia Meijer Phillip Glass: Metamorphosis
The Pentangle The Pentangle (SHM)
Rebecca Pidgeon The Raven
Pink Floyd - Dark Side of the Moon
Pink Floyd - Wish You Were Here
Poco Pickin Up the Pieces
The Police Every Breath You Take
Queen Greatest Hits (SHM)
Queen Greatest Hits II (SHM)
The Police - Outlandos D'amour
Steve Reich Music for 18 Musicians
The Rolling Stones - Beggars Banquet
The Rolling Stones - Let it Bleed
The Rolling Stones Sympathy for the Devil
Steely Dan Aja (SHM)
Steely Dan - Gaucho
Sting Sacred Love
Super Furry Animals - Love Kraft
10cc - The Original Soundtrack (SHM)
Tiny Island Tiny Island
Tomita Clare de Lune
Tomita The Planets Ultimate Edition
Vangelis Blade Runner Soundtrack
Jeff Wayne - War of the Worlds
Junior Wells Come On This House
Stevie Wonder - Talking Book (SHM)
Stevie Wonder - Innervisions (SHM)
Stevie Wonder - Fulfilliness First Finale (SHM)
Stevie Wonder - Songs in the Key of Life (SHM)
Yes Fragile
I used to have a surround setup, but have recently gone all stereo again, but if I ever move into a larger flat and can accommodate stereo and surround (in a way that allows both to be heard in all their glory), I'd have surround again because there have been some great multi-channel releases in both formats.