I've seen people put the Accelero Extreme III on there with good results. Be careful as with some cards (XFX maybe?), removing the factory HSF voids the warranty.
I can't remember what the Acceleros cost and what temps they produced, but another option would be to buy just the cooler (if you can find one on ebay or somewhere) from a Sapphire Tri-X. They seem to be killing it in terms of air cooling for the 290s.
http://www.tomshardware.com/reviews/r9-290-accelero-xtreme-290,3671-4.html