I use 1D2 bodies. I don't think there's anything a whole lot better out there for low light focus.
When the light drops, I use the center focusing spot and put it on something contrasty -- a man's shirt and necktie, or a white nametag on a dark suit. Also, in my experience One Shot AF takes a long time to lock on, while continuous focus used in conjunction with the thumb button (* button for focus) is quicker and can be more accurate. Or maybe accurate enough. If it's pitch black, then you need the focus assist beam on the flash, which works with One Shot AF.
I usually end up shooting at 800 or 1600 ISO, at about f/2.8 or f/4. I try to keep the shutter around 1/60, but I'll drag it as low as 1/15 to get the background to open up a bit. That said, my best photos come from using a second flash to light the background and rim light the subject. Not always possible, of course, but it works well.