When I did this, I just grabbed a cheap set of Forte Metro-K slicks from my local Performance Bike. They worked well, but wore a little faster than I liked; given the dirt-cheap sale price, it's hard to complain too much, though. Next time around, I'll probably try the Ritchey Tom Slick or Forte Slick City.
For mixed pavement/path/gravel riding I've been using the WTB All Terrainasaurus which seems to work very well.