I'm rarely useful on this board, so here's a pretty complete list of what I think is good in this quasigenre.
Aftermath - Eyes of Tomorrow
Annon Vin - A New Gate
Believer - everything
Calhoun Conquer - Lost in Oneself
Coroner - well, you know
Deathrow - Deception Ignored, Life Beyond <- Deception Ignored is my second pick in the genre. A real gem.
Depressive Age - First Depression, Lying In Wait, the rest of the stuff is marginally there
Flaming Anger - two demos, excellent.
Hexenhaus - Awakening (a bit more power metal than the rest)
Invocator - Weave the Apocalypse
Kinetic Dissent - I Will Fight No More Forever
Megace - Human Errors
Mekong Delta - everything
Mordred - Fool's Game
Realm - Endless War, Suiciety
Sieges Even - Lifecycle <- my first pick
Spiral Architect, marginally, mainly because they're Watchtower clones
Toxik - Think This
Tourniquet - I'd say everything besides those awful middle two albums
Watchtower - more Energetic Dissasembly than Control and Resistance
Windham Hell - everything
Zero Hour - A Fragile Mind, Metamorphoses
Closest bands these days with a strong technothrash influence would be stuff like Verse and Radiation, Keelhaul, possibly Behold the Arctopus, but I wouldn't say directly. By way of Voivod mostly, which isn't really in this subgenre. And there's a whole host of math-inspired bands that really don't have anything to do with this, although they sound it.
azal: steps, the second Sieges Even record has absolutely nothing to do with watchtower, or in fact, metal. It's colder, more complicated Rush. Confessor are totally technical but not thrash. Techdoom would be their own little genre and they're alone in there along with Loincloth and I guess the first Memory Garden record.