Here is a review of the HD5570:
http://www.silentpcreview.com/ati-5450-5570
It is bus powered,low profile,has a single slot cooler and has similar performance to a HD4670. However load power consumption is much lower.
Also the GTS250 low profile card is also available:
http://www.cclonline.com/product-inf...67&tid=gsearch
http://www.cclonline.com/product-inf...68&tid=gsearch
However it requires a PCI-E power connector and has a double slot cooler.