Pretty much the entire Metalcore/Deathcore genre for me. Metalcore and deathcore were cool when they were a lot more underground and there was actual thought in their songs rather than:
"Dood, Lets like totally put a breakdown into a breakdown into another breakdown while some underage girl fawns over my straightened fringe!"
"YEAH!"
August burns red are good (though don't listen to them much at all, but from what I have listened to, They good

) and Old Killswitch Engage(Pre 2nd Self titled album... I mean really, who makes
2 self titled albums?) were good, and I like a bit of Black Dahlia murder from time to time but the 2 genres have generally gone downhill since my generation (the 14-17 year olds) got into them for the moshes, the "Metal" scene, and to look cool and all expressive over how "Depressed" they all are, and it still drives me crazy that
NO ONE CAN FUCKING DISTINGUISH BETWEEN METALCORE AND TRUE HARDCORE THESE DAYS
Well what my generation did to metalcore is partially the reason why I am a prog-metalhead primarily.
Though a bit more on topic as a final note: some of the more mainstream Nu metal bands (yes, I like Nu Metal, it just got tainted by awful rap metal for so many years that it never got to shine as it should have, as in, rhythm based metal, but it never shook that rap-metal image sadly... *Sigh*)Korn and slipknott.
Seriously, Whatthefuck guys? Whatthefuck? After Take a look in the mirror, Korn Just went shit, with no depth to them at all. Despite what anyone says I think that Twisted Transistor was a SHIT song, and it went further downhill from there. Also, Head was probably their saving grace musicaly.
Slipknot on the other hand... well I did like them (along with Korn) when I was 10 (Shit, that was 7 years ago...) and they were fun then... And this is going to sound really hipster, but they seemed to get worse when more people started liking them... As well as every album they made post Subliminal verses... (though I am mixed on SV)
But yes, thats my long arse TL; DR Metal Rant.