I know the opinions on these bands tend to vary, but easily two of my favourites are Bonded By Blood and Fueled by Fire. Their debut albums are both wonderful.
Then also check out Violator from Brazil, they have an awesome full length called Chemical Assault.
Bywar, also from brazil, have 3 albums all of them good to great.
SSS, (short sharp shock) from the UK are crossover thrash, similar to municipal waste. I PERSONALLY think they're just as good. they also have a full-length with another one on the way soon, apparently.
Hatchet are an awesome Bay-Area-style thrash band from the U.S. They have an album released a few months ago, it's called Awaiting Evil and it has some excellent lead guitar playing all over it.
If you like your thrash really fast and raw, check out Merciless Death. They have two full-lengths, the second one is better for my money.
There's also a band called Victimizer from Denmark. They have a very solid full-length released last year called the final assault. I think they broke up though.
All the other bands mentioned here so far are REALLY great as well, so don't think i'm dissing them or anything, im just trying to mention ones that no one else has. The only one out of all the bands mentioned here that I dont really like is Avenger of Blood. I have their second album, Death Brigade, but it just never clicked for me.
I haven't yet had a chance to check out Head-on Collision or Hexen, but based on the reviews on this very site, I very much plan to.