You probably know this already, but in order for a drummer to play acoustic drums at a lower volume, he must also alter the way he plays. Given that starting point, there are a few methods that will help keep your volume down without sucking the life out of your playing, or the drum sound. You may need to make a few small investments though.
Sticks: You will need lighter sticks. Try some thin sticks that are fairly long, so they feel more natural in your hand. I use Vic Firth AJS when I want a normal feel with a little less volume.
Cymbals: A flat ride allows you to play normally without a lot of volume or wash, although you won't have a bell if you need it. Smaller (15 - 17") thinner crashes are darker and sound big, but with less volume. 13 or 14" thin hats will also help keep the volume under control.
Kick: I hate to say it, but muffling the kick and using a felt beater is the best way to keep your volume down while still playing naturally.
Snare: Most of the perceived volume comes from attack, either from the head, or the way you play. I suggest muffling the drum a bit, but not so it's dead. Also, tune the batter down a bit so there's not as much high-end (attack) when you play (a 2-ply coated head will help mellow the brightness.) But, you want the snare to cut, so here's how to bring back the attack without the actual volume - play some rim, but control the stroke. This is the one instance where you'll want to deliberately shorten the stroke, but it will sound like you're hitting the drum hard... just without the volume.
Toms: Gotta muffle them too, but not too much. Like the snare, a 2-ply coated head will help curtail attack. Tune them on the low side, as the resulting volume will seem to be lower. *
And if you have the option, use slightly smaller drums. I have a wonderful 20/12/14 kit that I use for quiet clubs, but may bring a 24/14/18 to larger venues with the same band (they never really know what kit I'll show up with!)
Still, you'll actually need to play lighter, there's no getting completely around that. But these methods will help you retain as much natural motion as possible, and it should be easier for you to sound like you're rockin' without getting chewed out for it.
Bermuda
* Conversely, in situations where you need more volume, you'd generally do the opposite - tune drums higher, use clear batters, plastic beater, med-heavy cymbals, etc.