Loudwire.com has put together a list of the Top 50 Metal Songs of the 21st Century.  They took several things into account, including "innovation, significance, influence, commercial success, critical praise, fan reaction and subjective opinion." 

It was limited to one song per band, and stuck to their definition of "metal," and left out stuff that's more hard rock and punk. 

Here's the Top 20:

1.)  "Lateralus",  Tool  (2002) 

2.)  "Blackwater Park",  Opeth  (2001) 

3.)  "Colors",  Between the Buried and Me  (2007) . . . It's a 65-minute, album-length song broken up into eight parts or tracks.  So it's arguably more of a concept album than a "song."

4.)  "The Talisman",  Iron Maiden  (2010) 

5.)  "Toxicity",  System of a Down  (2002) 

6.)  "Make Them Suffer",  Cannibal Corpse  (2006) 

7.)  "Fault and Fracture",  Converge  (2001) 

8.)  "The End of Heartache",  Killswitch Engage  (2004) 

9.)  "The Heretic Anthem",  Slipknot  (2001) 

10.)  "Disciple",  Slayer  (2001) 

11.)  "Everytime I Die",  Children of Bodom  (2000) 

12.)  "Blood and Thunder",  Mastodon  (2004)

13.)  "Revolution Is My Name",  Pantera  (2000) 

14.)  "Piss Angel",  Pig Destroyer  (2001) 

15.)  "Bible Black",  Heaven & Hell  (2009) 

16.)  "Progenies of the Great Apocalypse",  Dimmu Borgir  (2003) 

17.)  "The Beginning and the End",  Isis  (2002) 

18.)  "Apathy Is a Cold Body",  Poison the Well  (2003) 

19.)  "When Good Dogs Do Bad Things",  The Dillinger Escape Plan  (2002) 

20.)  "Redneck",  Lamb of God  (2006) 

The complete list is up now at Loudwire.com.  It includes brief write-ups on each song, along with YouTube links to the audio.  It's a long slideshow . . . but there are links to take you to the Top 20 and Top 10.)