I'm partial to new metal (nu metal?). Modern metal with a lot of grunge influence is more my style (you can tell I'm a child of the 90's), but I'm not a major fan of grunge rock music alone (Nirvana, Pearl Jam). Don't get me wrong, I love everything Metallica, but I've embraced the albums from the Black album to the present, and most "metal heads" haven't.
Some of my favorite modern mainstream metal:
System of a Down:
http://www.youtube.com/watch?v=CSvFpBOe8eY
http://www.youtube.com/watch?v=iywaBOMvYLI
Korn
http://www.youtube.com/watch?v=jRGrNDV2mKc
RHCP
http://www.youtube.com/watch?v=Mr_uHJPUlO8
Monster Magnet
http://www.youtube.com/watch?v=dscfeQOMuGw
Powerman5000
http://www.youtube.com/watch?v=lsV500W4BHU
Godsmack
http://www.youtube.com/watch?v=1uvwG...=TLStTJLxmf1P8
and my favorite Metallica:
http://www.youtube.com/watch?v=WM8bT...=TLwySEsy3F9Cc
http://www.youtube.com/watch?v=1QP-SIW6iKY
http://www.youtube.com/watch?v=boanu...=TLuVruiYxutGs (LOVE this one!)
http://www.youtube.com/watch?v=Fd9oh...=TLVPCq0GHbWsk (metal + symphony orchestra = love)