Josh, if you absolutely must use a flash, get a 430EX, try dialing down the output to anywhere from -1 to -2, and use some kind of pocket modifier (the Lumiquest Big Bounce worked amazingly well for me when I shot in these situations - very soft, natural-looking light for a flash). And maybe use a CTO gel over the flash head.
Cranking down the shutter is often a good idea, as well.
And if you can (in the future), for the love of God, get an off-camera cord or an STE-2.
Of course, unless the lighting is really awful, I'd probably sooner crank up the ISO to 1600 and shoot au naturale.