I found that most of the energy in Origin is set by the furious drumming of John Longstreth. I'd suggest looking up his other projects: Angelcorpse, Dim Mak (newest), Skinless and such. Looks like it's going to be the best/only advice you get in this thread.
Unmerciful are pretty much origin part 2, two ex origin members play in the band. I'm sure there are loads of origin clones out there since their so popular at the mo!
While not being origin clones at all, crimson massacre and ulcerate should do it for ya.