Lets see…
George Clinton and Funkadelic (x2)
Tool
Red Hot Chili Peppers
The Mars Volta
A Perfect Circle
Soulive
Disco Biscuits
Medeski Martin and Wood (x2)
The Flaming Lips
String Cheese Incident
GWAR (I dont like the music, I went for the show. And my god, did I ever get a show.)
There are some others I can’t think of right now.
This summer I will be seeing Lollapalooza and the Allman Brothers as well.
My highlights:
Mogwai
…And You Will Know Us By The Trail Of Dead
Kronos Quartet
Diamanda Galas
The Residents
Spearhead
Karl Denson’s Tiny Universe
Love
Etta James
Eddie Vedder
Philip Glass
Stevie Wonder
Classical:
Isaac Stern
Golub/Kaplan/Carr
Anonymous 4
Pop/rock:
Crosby, Stills and Nash
Kansas
Yes
Indigo Girls
Ani DiFranco
Weezer
No Doubt
Barenaked Ladies
Jazz:
Woody Herman
Maynard Ferguson
Wynton Marsalis
Spyro Gyra
Pat Metheny/Ornette Coleman (the Song X tour, which I didn’t appreciate until much later)
Lincoln Center Jazz Orchestra
Sonny Rollins
Steve Lacy
Maria Schneider
Sphere
John Zorn Masada
Bill Frisell
World Saxophone Quartet
Toots Thielemans
Hank Jones
Marian McPartland
Brad Mehldau
Steve Turre
Kenny Drew, Jr
Tim Warfield
TanaReid
Joanne Brackeen
Paul Bley
Jessica Williams
Willem Breuker Kollektief
Elvin Jones Jazz Machine
Fred Hersch
Jane Ira Bloom
Julian Priester
David Murray
McCoy Tyner
Kurt Elling
Stanley Cowell
Dave Frishberg
Ravi Coltrane
Barry Harris
Danilo Perez
Ray Brown
…and more I’m probably forgetting (I’m mainly a jazz fan, obviously)
Oh hell…here’s some more…(I really should keep a log)
Tori Amos (2x) (g.f. made me go)
Rusted Root
Foghat (yes, “Slow Ride” Foghat)*
Big Ass Truck (2x)** (these guys were the chicken-fried best)
Greg Allman Band
Luna* (very fun show at the Somerville Theater)
Andy Somers
The Cranktones (countless times at Toad)*****
Barrence Whitfield and the Savages (many, many drunken nights at Toad)******
The Tarbox Ramblers*
Angry Salad
Luscious Jackson
G. Love and Special Sauce*
I’m sure there’ll be more.
In order as first seen, from fourteen years old or so. The ones you don’t recognize may have been local bands:
Billy Joel (sis took me)
The Who
Molly Hatchet/April Wine (hey, I was a KID!)
Rush (fell asleep, I think that everyone else did except Coldfire)
Degenerates
Really Red
Mydolls
Culturcide
Green on Red
Meat Puppets
Zeitgeist (not the Reivers)
Dream Syndicate
Minutemen
Dammed
Big Boys
Dig (~50X)
Modern English
Replacements
Technicolor Yawns
Dharma Bums
Cargo Cult
Daniel Johnston
Texas Instruments
Glass Eye
Pez
Doctor’s Mob
Javelin Boot
Offenders
U-men
Hickoids (~300,000X)
Ideals (~300,000X)
Nice Strong Arm
100th Monkey
FAF!
Femme Fatale
Flaming Lips (they did Tommy, the whole opera)
Sonic Youth
Scratch Acid
Miracle Room
Butthole Surfers
Grateful Dead
GWAR!
Bouffant Jellyfish
Retarded Elf
Bad Mutha Goose
Willie Nelson
Motorhead
Moody Blues
Neil Young and Crazy Horse
(Are you reading this post?)
Balloonatic
Storyville
Robert Earl Keen
Toni Price
Asleep at the Wheel
(Are you reading this thread?)
(The following were seen when working at a concert arena)
AC/DC
Aerosmith
Alabama
Amy Grant
Motley Crue
Metallica
Pink Floyd
Robert Plant
Bruce Springsteen
Van Halen
Somewhat in order:
Ozzy (4x. The first was with Randy Rhoads, wonderful show! Then Randy died a month later 
This was my first concert)
Rolling Stones (3x)
Rush (6x. Have tickets for two of their shows on this tour too! Did I mention that they’re my faves?)
Metallica (4x. The first on their Master of Puppets tour, with Cliff Burton on bass.)
Journey
Foghat (Excellent, fun performance!)
Donny Iris (Well, he opened for Journey)
Sammy Hagar
Zebra (opening for Sammy Hagar)
Fishbone (2x)
The Fabulous Hedgehogs (opening for Fishbone)
J. Geils Band
The Chieftans
George Thorogood
Iron Maiden
Scorpions
Primus (opening for Rush)
Heart
Psychadelic Furs
The Blow Monkeys (Opening for the Furs)
De La Soul (Opening for Fishbone)
Boston
The Who
Pink Floyd
The Fabulous Thunderbirds
Living Color (Opening for the Stones)
Green Jello 
Gary Moore (Opening for Rush)
Mr. Bungle
The Grateful Dead
Aerosmith
Guns 'n Roses
ZZ Top (2x)
Ted Nugent (that guy seriously needs to shut up and play his guitar!)
Spinal Tap (On the Break Like the Wind tour, no less.)
Keef Richards (on his Expensive Winos tour.)
Van Halen (With Hagar on vocals.)
Candlebox (2x. The first time they were great. The second time, they were a “last minute emergency” opener for Metallica, because the original opener, Alice in Chains, was unable to perform. They (Candlebox) had a bad show this time.)
Tool
Suicidal Tendencies
Screamin’ Cheetah Wheelies (Memorable because other audience members and I spent their set making fun of the falling down drunk lead singer.)
Paw (They were fun!)
Bryan Adams (OK, OK. The tickets were free, alright? Besides, it was a good show.)
Winger ::shudder:: (They were opening for Scorpions. Butt rock extrordanaire.)
…and of course I was at Woodstock, weren’t you?
Forgot Motorhead!
Lemmy croaking Ace of Spades into an elevated mic is a must see!
OK, this is a short list.
Voodoo Symphony (DMB cover band, basically)
3 Doors Down (Shinedown and Tantric opened)
Metallica (Godsmack opened)
A bunch of local bands that I helped roadie/tech for because they were friends or relatives.
Rawlins Cross, 1996
Tori Amos, 1997 and 2000
Ashley MacIsaac, 1998
Alanis Morrissette, 2000
Wide Mouth Mason, 2000
Dar Williams, 2001
Madonna, 2001 and 2004
Sarah McLachlan, 2004
In a somewhat random order:
AC/DC
Scorpions
Megadeth
Metallica x2
Guns 'N Roses x2
Aerosmith x3
KISS x2
The Offspring
Everclear
Def Leppard x2
Bon Jovi
Jackyl
John Michael Montgomery
Alabama
Gwar (Milwaukee Dopers, is the Odd Rock Cafe on KK still open?)
Slayer
Death
King Diamond
REO Speedwagon
Styx
Ozzy x2
White Zombie
Rob Zombie
Bob Dylan
Tracy Chapman
Inner Circle
Night Ranger
Foghat x2
Motley Crue x3
Poison
Warrant
Boston (second time next month)
Cinderella
Ratt
Grateful Dead
I’m sure there are some I’m missing, but it’s a start.
Oh, and favorite show? Grateful Dead, *Touch of Grey * tour. 16 and first acid trip.
Biffy, are we twins separated at birth? I remember Head Hands & Feet! Didn’t they open for BS&T? Sheesh, the old days…
God, I’m forgetful.
“Weird Al” twice
The Monkees twice
RAY CHARLES, on what ended up being his last tour.
When I saw 'em, they were opeing for Tull on the Thick as a Brick Tour. “A song for Suzie…”