Too easy.
- Been around since early 90's, went big as far as the European Thrash scene went with Heresy, took a break then came back with Collision Course, took ANOTHER break and then went back to being a band again. They even have a new album out in 2012, Tales of the Weird.
Deathrow - One word.
- Did a number of great Tech Thrash releases, my favourite being their first one First Depression, then after Electric Scum fell off the face of the earth.
- Not a death/thrash fan, but their two releases A Shedding Of Skin and The Heritage are massive and rare as it is, plus its got so much power. If you want something of a slightly different quality, their other two releases are good.
Vendetta - My favourite german band, bar none. Go and Live, Stay and Die are among some of the tastiest tech I've heard with fantastic riffs. Brain Damage is a bit simpler, BUT it has some REALLY nice gems (War, title track, FADE TO INSANITY). Admittedly, their recent ones are average and make me want to cry since they're the guys that did Suicidal Lunacy AND Drugs and Corruption...
BTW, only Exumer was the only band I was willing to use. Necrophagist are time wasters for this. Helloween, on the other hand, is a good band but I never listened to them.