These brifters should pretty much work with any shimano road RD from the indexing era with a minor exception of some late 80s dura ace stuff, I believe. I've had these same brifters and run them with the matching RD, a 7 speed shimano light action RD from the mid/late 80s, a 105 10 speed RD, and, currently, a Deore XT RD I picked up last year (if switching to mountain RDs, most will work, but check because some of the new designs are a little different). My understanding is that as long as the pull ratio is consistent (and it is with Shimano with those few exceptions), the RD doesn't really care how many speeds you have - provided the RD has enough range to cover all your gears. So, if you want new, any of the road 10 speed stuff will work. At the same time, you shouldn't have any trouble finding used gear that will work if you want to go the e-bay/craigslist route. A nice, matching, Ultegra 6500 RD, would be a lot cheaper than something new and still work very well.