My un-armed system of choice is WW-II Combatives (mostly, some JKD and general tidbits worked in here and there too. If its "dirty fighting" odds are I practice it, which brings me right back to WW-II combatives)....
BUT, I dont like WW-II Combatives knife methods... except perhaps Fairbairn's smatchet stuff. Its too specialized, and requires itself to be too precise for the street I think. Great for taking out sentry's and doing assasinations, but not a street thing... ya get me?
For that... well... A healthy dose of James Keating, Jerry VanCook, Bob Kasper, and Kelly Worden. Mix that with Don Rearic and SouthNarc from SelfDefenseForums.com, and you've got what I train in.
Basically it boils down to simple, effective, methods of dispatching another human being, using an edged weapon. Gross muscle movement, strong powerful attacks, reverse grip ripping, not slashing (Pikal reverse grip, with the edge in), etc. It works with what I carry, which is folders and fixed blades with blades 6" or less. Works with bigger stuff too... thats where another big dose of Keating comes in. Mix bowie stuff with close range stuff, ohh... fun.
No formal classes, I train at home, funds and ability to travel have no permitted me to go to courses, and there are no local dojo's provide what I am after.
I use foam and cardboard cutting targets to practice on, and spar with others using training knives when I get the chance,