At the LBS I flexed some non disc aluminum racks to the width they would need to be in order to clear discs and it just felt like a little bit too much stress to put on the racks.

I just bought a Planet Bike Versa Rack that is supposed to work well with dics. Unfortuantely I am still waiting for it to arrive. I leaned away from the Topeak stuff since it is set up to accept Topeak bags. Of course you don't have to buy a Topeak bag, but looking at that part of the rack every day would kind of bother me. Just look around at some online bike stores and I'm sure you'll find plenty of options.