Some newer racks attach directly to the seatpost only, but for the most part they don't work with panniers since there are no rack struts to keep the panniers away from the wheel. However, I did see one of these racks, perhaps Delta, or Topeak, at REI recently and it had some rigid tubing that hung below the rack on each side to prevent the panniers from swinging into the wheel. There are also some more traditional racks designed for bikes without eyelets and traditional seat stays that use various adapters to attach, but have no idea how they work.

Another option would be to use a rear rack pack instead of panniers - some of them are fairly large now, and combined with a front handlebar bag, might do the trick. Remember to keep the loads light with this setup as it will affect your handling. One reason Panniers work so well is because they keep the weight low. Even with that, loading rear panniers too heavy can also cause problems. Oh, and remember if you decide to try panniers on a road-racing style bike which has shorter chainstays, that you may run into a problem with your feet hitting the bags at the heel. Touring bikes generally have longer chainstays for that reason.

If you have not made a bike purchase yet, you may want to consider a bike that is more traditional in the sense that it is not a full-blown loaded touring bike, but still has mid-length chainstays and relaxed geometry, perhaps steel for a good ride, and it might even come with rack eyelets! Something along the lines of the Bianchi San Remo (not sure if still made) or a cross bike.