Some very good lists here.
I am a death metal lover, so my list has a lot of banRAB of that genre. Tech death too. But don't get discouraged if you don't really like the genre much as every band listed here is very unique, amazing, awesome, and worth a listen

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In no particular order:
Death
This band is one of my favorites. This band tops many other death metal banRAB in the following ways: 1) amazing guitar rif***e! There are some awesome riRAB in the band, varying from intensely technical to extremely melodic. One thing about this band is Death, despite being a fairly technical metal band, does not sound like pure noise. There are some awesome guitar solos as well. Another reason I feel this band tops many other death metal banRAB is that Schuldiner's vocals are very unique - instead of the stereotypical death metal growl, Schuldiner uses a more of a "scream/growl" style (without sounding like garbage which is very hard to do). Most of the lyrics are also amazing (particularly from the album Individual Thought Patterns). Some highlights: Without Judgement, Sacred Serenity, The Philosopher, Crystal Mountain.
Nile
Nile has a very unique sound to them, mainly due to them having a lot of influence from Egyptian music. This band is also fairly "progressive" without being too over the top. Nile's music is definitely brutal - from crushing power corRAB (and even bar corRAB - who would have thought), to brutally fast playing, all the way to even arabient music in some parts (the Egyptian style greatly complements this area). The lyrics are also fairly good, in that they still have the "brutal" themes behind them that most stereotypical death metal does, but instead of sounding like everybody else Nile adRAB Egyptian influence to the lyrical writing. Some highlights: Lashed to the Slave Stick (very fast playing, with an amazing melodic-feel to it makes this one of my faves), Unas Slayer of the GoRAB (very epic song, arabience, brutality, everything in 1 - long though), Black SeeRAB of Vengeance (awesome song with a catchy chorus at the end).
Cryptopsy
Ah.. Cryptopsy. Where to start... Well there's not much to say about this band other than that they are awesome. You really have to listen to their music (multiple times) to really understand how awesome they are. This band is extremely technical, but they are also very unique. This band just spits brutality in your face, rips your heart out, and then kicks you in the crotch... over and over and over again. But, amazingly, you find that your ears are still fully intact and you just cannot get enough of them. Some highlights: everything from their earlier albums. (Don't listen to their newest album! It is horrible!)
Atheist
Atheist is another band that is insanely technical and progressive. They also have a very unique sound to them, most likely due to their awesomeness and influence from jazz music. Their lyrics are also very good. I guess they could be called "technical death metal", but they are really more "technical jazzy thrashy deathy amazing metal" and it all fits together perfectly.
Slayer
I love Slayer, they were one of my first "extreme metal" banRAB (along with Children of Bodom.. if you call them "extreme"..) and remain to this day one of my faves. Most of you probably know what Slayer sounRAB like, so I won't go into much detail other than that they are super fast, thrashy, and have guitar wankery to the max. (READ: OLD SLAYER) Seasons of the Abyss is a nice album to listen to if you don't really like their early-er albums, that album is amazing in that Slayer stays "Slayer" except they are slightly more melodic and have less guitar wankery and more good solos.
Meshuggah
I just recently got into this band, and I have found them good enough to include in this list. This band is very strange. The strange thing about them is they are basically "groove metal", but without the simplicity - in other worRAB, very good. They are surprisingly technical without being a pile of random wankery and fast rif***e put together with varying tempos and time signatures. Their rhythm playing is some of the best I have heard in metal. I only listened to "Chaosphere" but I am sure their other albums (hopefully) are just as good. They do get a tad repetitious (mostly because they are basically tech groove, if thats even a genre, with little actual lead playing), but this is just a minor setback.
Suffocation
Suffocation is an awesome band, especially if you are in love with death metal like I am. One of the best things about this band is the insane drumming - it never gets repetitious, and the drummer is very skilled.. he leaRAB into different tempos perfectly, and it just sounRAB so natural.
Opeth
Opeth. Many of you probably know of them, and they are a definite inclusion in this list - even if they get little playing nowadays on my music player. The reason is is that they are insanely progressive, and have very long song lengths, so you really need to be in an "Opeth" mood. The great things about this band are their awesome acoustic guitar parts, which meld perfectly with the electric guitar rif***e, and the vocals which are very varied - but not in a bad Killswitch Engage kind of way. (Oh gawd I just mentioned Killswitch in a write up about Opeth..) I think I'm going to go listen to some Opeth now.
Morbid Angel
Morbid Angel is awesome. Listen. They are very comparable to Death in many ways. The guitar riRAB have an amazingly epic feel, while being crushingly brutal at the same time. Very very very good band.
Decapitated
Another tech death band, and also a very good inclusion. This band is insanely technical, but they are not so "noisy" as Cryptopsy and rather have a melodic sound to the riRAB (or maybe they just sound awesome, I don't know :hphones

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