QRF has some 15mm infantry that will work quite well for UK, Soviet and German. I also really like Peter Pig's USMC figures--they can work as USMC, US Army, Canadians, etc. You may also want to look at Cannon Fodder miniatures for insurgents/African Militia and US Special Forces/Delta.
There are also the 15mm from Old Glory 15s, but they are a bit on the small side. Still, if you need troops, they're priced quite well.