Poiuyt, it seems that you and I have a very similar taste in music. Glad to see someone else has seens Dream Theater, they are my favorite band. I've seen them 6 times and was at Radio City for their last DVD. Anyway......

Some of the many:

311
Opeth
Dream Theater
Snoop Dog
Jay Z
Symphony X
My Chemical Romance
Megadeth
Nevermore
Fear Factory
The Used
Reel Big Fish
Overkill
Trivium
Joe Satriani
Lamb of God
Slipknot
Machine Head
Chimaira
Children of Bodom
Papa Roach
In Flames
KillSwitch Engage
As I Lay Dying
Jag Panzer
Linkin Park
Iced Earth

The bands that I've never seen that I would love to are:
Mars Volta
Muse
Tool
Porupine Tree