Liquid Tension Experiment
Dream Theater Drummer Mike Portnoy once decided to try and get a band together and write and record an album in like a week's time or something. So he got together with bass god Tony Levin, keyboard wizard Jordan Rudess (who at the time was not part of Dream Theater) and DT Guitarist John Petrucci to put out The Liquid Tension Experiment.
The album that resulted from this is chock full of progressive musicianship, and even a little bit of Chapman Stick. Paradigm Shift, Universal Mind and Stretch are awesome tunes, and who doesn't like a little bit of Jazz Oddyssey in the form of Three Minute Warning.
This album isn't an everyday listen, but when you're in the mood for some crazy instrumental goodness, it certainly hits the spot.