I came close to replacing my pickups with a set of Duncans. They have a lot of good info on their web site, plus they also sell a CD that has samples of all their pickups. Being able to hear the pickups you're interested in is a big help, so I'd recommend doing that somehow. If you can't then make sure you like the company's return policy (and Duncan has a good one).
I ended up going a different route than most people and bought active single coils - an EMG David Gilmour set. It's not that I was dying to sound like Gilmour. I liked how the pickups sounded despite some people saying they sound "sterile" compared to regular single coils, plus I liked the add-on preamps that came preassembled on a pickguard. One is a presence booster that also cuts the highs and lows, giving the guitar a fatter sound. The other add-on does just the opposite - boosting the highs and lows while cutting the mids so you get an even glassier single-coil tone. These gave me the flexibility of being able to get a nice single coil tone and also a fatter humbucker-like tone (especially when I turn up both tone controls) from the same guitar. At $229 it was a lot cheaper than buying a 2nd guitar.
Lots of choices out there. Have fun checking them out.