I love Exhorder and I enjoy some Pantera. What else should I listen to? The more thrashy, the better. I already listened to Machine Head's debut album. I had great expectations (since I am a great fan of Vio-lence too) but frankly I was rather unimpressed. Something else?

Machine Head's latest album is a lot more thrashy than all their albums combined, still groove metal. Give that album a shot. Have you given Prong's 90's stuff a try? If not, go for them. The stuff's basically somewhere between Industrial, Groove and Thrash

Maybe Pro-Pain - Contents under pressure
Groovy, thrashy hardcore.

Maybe try some Helmet?

Chimaira may be what you're looking for. I see them being labeled metalcore a lot, but I hear a lot more Pantera and Fear Factory than Killswitch Engage in their sound. Their debut may be a bit more nu-metal oriented than what you're looking for and their latest I find a bit weaker than their others, but anything in between is solid stuff, well worth checking out. While not one of my favorite bands per se, I give them credit for having a very unique sound.

And of course, Fear Factory's Demanufacture and Obsolete in case you haven't heard them. Soul of a New Machine is to be counted among their classics as well, but it's also much more death metal-oriented.

Most of Overkill's post-Horrorscope stuff is a combination of thrash and groove. I Hear Black, Killing Kind, From the Underground and Below and Necroshine, which is my favourite Overkill album, are all great albums, with plenty of groove/thrash riffing.

It's not thrashy at all, but I cannot recommend White Zombie enough. Seriously. There Grooves stuff can be heard on Astro Creep: 2000 as well as La Sexorcisto, the former being the better oft he two.

Shatter Messiah's God Burns Like Flesh is groovy as hell and manages to remain menacing and aggressive.

Later Exodus

Gurd have some pretty good releases under their belt.

do yourself a favor and save yourself from some grief and ignore this post & the entire existence of Machine Head

look to Phil and Robbs first and infinitely better band, Vio-lence. their 3rd and final album 'Nothing To Gain' was real, ballsy, Groove-just like Exhorder, not blasphemous water-downed horsehit which is what you will get if you go to machine head

You've probably got it already, but Sepultura-Chaos A.D is a excellent groove metal album.

there are only a few groove metal albums i enjoy.

one of them is Chaos AD by sepultura
the latter half of forbidden's discography
and
demolition hammer's time bomb

for the rest there is not much worth checking out except the odd good groove metal songs by testament

Nothing to Gain is a giant pisstain on Vio-Lence's discography. They'd have been better off without that album. Ballsy? Only if you consider Pantera albums like "Reinventing the Steel" ballsy.

As much as I dislike many groove bands (Lamb of God and later Pantera, except for a few songs) when combined with thrash/death its fucking awesome.

God Dethroned - The Lair of the White Worm (album). More specifically check the songs Loyal to the Crown of God Dethroned, Last Zip of Spit and Salt in your Wounds.

Cavalera Conspriacy - Cavalera brothers from Sepultura here. Very enjoyable thrashy groove metal.
Gojira - Little different than your average groove band. They have a bit of an atmospheric touch and some death metal influences as well.
Breed (Nor)- Solid groove.
Grimfist - Not my thing but a lot of people like them.