I know Clutch always featured a Hammond B3 organ pretty heavily... I'm not into them, but my girlfriend is, and plays it in her car a lot. So that might be a starting point...
unless you're talking about more extreme stuff.... but what do you mean by organ? Like Hammond B3/Allman Brothers/classic rock organ, or SYNTHESIZER stuff, like Bodom or Old Man's Child?
I always thought Old Man's Child was really good with that... they feature prominent keyboard playing, but its not gay and stupid like Cradle of Filth. "In Defiance of Existence" is my favorite.... its totally awesome. The only drawback is that its almost TOO clean, because the end of the first track gets into this fucking HEAVVVVY segment with Nick Barker messing with the drummer rythms and it just doesn't have the balls of a more.... "atmospheric" and "organic" production, like on Incantation's "Onward to Golgotha" or Morbid Angel's "Formulas Fatal To The Flesh"