In no particular order-

RUSH*
Pearl Jam*
Smashing Pumpkins
Ministry*
SRV*
Black Crowes*
Roger Cray
Spin Doctors**
Motley Crue*
Van Halen*
Primus*
Tragically Hip*
Grateful Dead*
Kenny Wayne Sheppard*
Guns N Roses*
Judas Priest
Lollapallooza1 (a)
Lollapallooza2 (b)
Lollapallooza3 (c)
Death Angel
Jane's Addiction*
Flotsam and Jetsam*
METALLICA*
Bon Jovi**
Pink Floyd*
Whitesnake
Cheap Trick
YES*
OZZY*
ZZ Top*
Tangerine Dream
Triumph
Aerosmith*
DIO*
Tesla*
Def Leppard*
George Thorogood*
KISS*
Roger Waters
Eric Clapton*
Iron Maiden*
Scorpions*
AC/DC*

Other festivals with mulitple bands seen too (ie-Monsters of Rock '87 LA Coliseum), just many not as cool as the first few years of Lollapallooza nowadays..
(a)=Main Stage: Jane's Addiction, Siouxsie & the Banshees, Living Colour, Nine Inch Nails, Ice T & Body Count, Fishbone, Butthole Surfers, Rollins Band, Violent Femmes.

(b)=Main Stage: Red Hot Chili Peppers, Ministry, Ice Cube, Soundgarden, The Jesus and Mary Chain, Pearl Jam, Lush, Temple of the Dog.

Side Stage: Jim Rose Circus, Sharkbait, Archie Bell, Porno for Pyros, Basehead, Cypress Hill, House of Pain, Sweaty Nipples, Arson Garden, Seaweed, Seam, Boo-Yaa T.R.I.B.E., The Look People, Stone Temple Pilots, Vulgar Boatmen, Truly, Skrew, Tribe, The Authority, Samba Hell, Rage Against the Machine, Chris Cornell and Eddie Vedder.

(c)=Main Stage: Primus, Alice in Chains, Dinosaur Jr., Fishbone, Arrested Development, Front 242, Babes in Toyland, Rage Against the Machine

Side Stage: Tool, Sebadoh, Cell, Unrest, Mercury Rev, Mosquito, Free Kitten, Royal Trux, Tsunami, Mutabaruka, The Coctails, Scrawl, Luscious Jackson, Genitorturers, Truly, Eggs, Girls Against Boys, Thurston Moore, Glue, Karl Hendrick's Trio, Hurl

*=Saw more than once
**= Saw with a girl

:rolleyes: That's pretty much what I can remember, there were many others..