What kind of music do you improvise to and how?

I've started improvising to peyote music

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Something that hasn't been mentioned is open night Jams. I spent many years going to blues open nights and jamming with other musicians, it helps a lot especially when there is an audience to drive your concentration. 

I improvise to Miles Davis Bitches Brew, Jean Luc Ponty;s "Don't let the World Pass You By" with the band or Gypsy Queen where I get more into improvising reflections of John McLaughlin than Santana.I tend to play almost everything note for note for examples a daily routine is to play along with Echidna's Art (of you)....Don't you ever wash that thing? by Zappa. I'm always learning George Duke piano solo's on the guitar and adding his vocabulary to my improvisation. I tend to learn Pat Metheny pieces and I believe he might be a huge influence on my playing. I am not the greatest at playing outside the melody off the top of my head and my level of performance depends on the chord progression chosen by the band. I still have an influence of Steve Hillage in my playing or maybe Frank Marino. I like to think for myself when I improvise and over the years I have released or disregarded various approaches to my reflections of other players. Some days I spend hours playing Classical guitar or learning 14th century Asian music to escape the craft.

I improv over loops all the time. It's part of how I write. 

I usually loop my bass and jam with myself. And sometimes I record everything.

I never thought of jamming something else. I always just jam by myself. Sometimes I'll loop a chord progression on my delay or use my Electro-Harmonix Freeze or a drum machine.

I like to jam along to Phish, because some of their jams can go on for 40-50 minutes sometimes, though they're usually 10-20 minutes tops. Some Zappa jams, or funk bands are good too. I also, if in the mood, will improvise along with jazz like post-bop, cool, and hard bop stuff.