Brazillian Jiujitsu. Grant, check out what we are doing in the U.S. Army. It has proven to be very effective with CQB situations. The basis of it is BJJ. BJJ complements aikido very well as it is also based on controlling center and posture alignment and the feedback process is very similar. although the methodology for training is quite different. I have found it to be a wonderful complement as have others on the list.
For Army guys like us...if you are looking for down and dirty relevant skills, i'd highly recommend our U.S. Army period of instruction. We have several videos out, as well as a Field Manual if you want to see how we are doing things.
We have many testimonials of guys that have used in the past couple of years.
let me know if you can't see it. I can get to it from my IP address in Germany, but I may also have "certificates" laptop that allows me to view .army.mil sights here.