Parts in songs that reminds you of other songs.

Despised Icon - The Sunset Will Never Charm Us (large heavy riff near end)

sounds like

Sepultura - Roots Bloody Roots (large heavy riff near end)
 
Behemoth - Chant of the Eastern Lands (first riff with synths)

sounds like

Emperor - Cosmic Keys to My Creations and Times (starting at 0:43)
 
Slayer-Killing Fields (0:14-0:37) is identical to a song in either Doom or Doom II. My uncle has the song on his computer, and we compared them.
 
I noticed quite a few blatant Slayer riffs in Aura Noir's Black Thrash Attack, but I'm too lazy to listen again to find them.
 
The intro of hit the lights by metallica sounds identical with the intro of Agressive perfector by slayer . Or the other way around.

I am sure there are more but I cant remember them at the moment.

I saw an interview with Dave Lombardo where he admitted to ripping off the Hit the Lights intro for Aggressive Perfector.
 
Immortal - One by one at 1.01 (too many ones there) is very similar to their song 'Tragedies blow at horizons' at 5.09

Both are killer songs nonetheless :kickass:
 
I didnt hear it myself so I dont know which Bathory song. Just somebody mentioning Bathory ripped off that song. I dont think Metallica are great but that is one of their songs that I like.