Examples of bands/artists you can't mimic?
In a good way. You hear one of their songs and go "That's _______"
I'd have to say some pretty good ones are
Nirvana (Overrated band, but a good one nonetheless)
Marilyn Manson (Dark, creepy sound. His voice is identifiable)
Pink Floyd
Rammstein (Till Lindemann is the singer if anyone was wondering)
Others?