Another unit that is very similar to the JMP1 but with a littl more versatility is the Rocktron Pirhana
many suspected that Rocktron based it on the JMP1 but gave it a sweepable mid frequency to allow a more detailed sound
I have one in my rack and it's really rather good
I'd reccommend the Piranha over the JMP-1, especially if you're looking to do more high gain stuff. You could probably pick one up for cheaper as well.
Other preamps I'd suggest you take into consideration are the Peavey Rockmaster and Engl e530. Neither are MIDI, but they sound awesome.
Poweramps though will also have a huge impact on your sound as well remember, so make sure whatever pre you get, you pair it up with a decent (preferably) all valve poweramp.