Hmm, well Mindless Self Indulgence.. they're.. Different... but that's a very broad question.. if you're into rap then rock would be different, and vice versa.. Or are you after really original stuff, groups with their own unique sounds and stuff like that? If so then try some of these:
Tool - Schism, Stinkfist, Parabola, Aenema
A Perfect Circle - Rose, Noose, The Package, Pet
Rammstein - Du Hast, Mein Herz Brennt
Mushroomhead - Bwomp, These Dirty Hands
Aphex Twin - Windowlicker, Donkey Rhubarb, Come To Daddy
Radiohead - No Surprises, Street Spirit (fade out.), Creep