Updated whenever I make it to a concert...
Jack White
opening band
A Perfect Circle (opened for Korn)
Alkaline Trio (x2)
Amber Spyglass
The Aquabats (x2)
The Architects (opened for Flogging Molly)
Arctic Monkeys
Automatic Loveletter (at Warped Tour)
AWOLNATION
Bad Larry
Bad Religion
The Birthday Massacre
Blue Man Group Complex Rock Tour
Boston Pops Orchestra (conducted by John Williams)
Boston Pops Orchestra (conducted by Keith Lockhart)
Boston Pops Esplanade Orchestra (conducted by Keith Lockhart)
The Bouncing Souls (x3)
Broken Neck Lullaby
Carbon Leaf (x1.25)
Chromatics (opened for Hot Chip)
Club D'Elf (~2)
Coheed and Cambria
Cradle of Filth (at Ozzfest)
Covenant
Cursive (opened for A3)
The Dear & Departed (opened for A3)
The Dead Weather
Deerhunter (x2; opened for Spoon and ?)
Dillinger Escape Plan (opened for Thursday)
Disturbed
The Down and Outs (x3)
Dr. Madd Vibe
Dream Theater
Dysrhythmia
Earl Greyhound (opened for OK Go)
Endless Hallway (opened for Thursday)
The Exposed (at Warped Tour)
Extra Action Marching Band
Eyes Set to Kill (at Warped Tour)
Fake Problems (opened for Thursday)
Fear Factory
The Flatliners (at Warped Tour)
Flogging Molly
Frank Turner (opened for Flogging Molly)
Ground to Dust
Hacienda (opened for Kasabian)
Harlem
Hot Chip
Jess Power's Project (open for TMBG)
Jonathan Coulton (x2)
Kasabian
Kenny Muhammed: The Human Orchestra (opened for MSI)
Lights (opened for Owl City (sucked))
Koo Koo Kanga Roo
Korn (x2)
KMFDM
Marilyn Manson (x3)
Middle Finger Salute (at Warped Tour)
The Mighty Mighty Bosstones
The Mighty Regis
Mikel Paris (opened for Carbon Leaf)
Mindless Self Indulgence (x4.5)
Motion City Soundtrack
My Chemical Romance (opened for MSI)
Neon Trees
New Riot (opened for Streetlight)
Nine Inch Nails (x3)
Of Mice & Men (at Warped Tour)
Off With Their Heads
The Offspring
OK Go
Orgy (opened for Korn)
Owl City
Ozzy
Paper Route (opened for Owl City (also sucked))
Paul and Storm (opened for JoCo)
Platform One (opened for The Bouncing Souls)
Reel Big Fish (x3)
Rob Zombie (x2)
Robert Francis (opened for OK Go)
Rodeo Ruby Love (opened for Streetlight)
Rogue Wave (opened for TMBG)
Saul Williams (opened for NIN)
Spoon
Streetlight Manifesto
Suburban Legends
System of a Down (opened for Fear Factory)
The Bobs
The Sparring (at Warped Tour)
They Might Be Giants (x4.75)
Thursday
Tim Minchin
Tim Blake (opened for Carbon Leaf)
Tripod
Tool (x2)
Tori Amos (x3)
Twitch the Ripper
The Union Underground (opened for Manson)
The Vaccines (opened for Arctic Monkeys)
Victor Wooten (x2)
Missing numerous opening acts, bands heard in bars et cetera, and bands watched for a few songs at festivals.