VR Zone reports AMD is working on the ATI Hemlock, a dual-GPU version of the Radeon HD 5870 that should arrive in November/December for under $500. Check out their site for more details.
From the information we gathered, the Hemlock card is slightly longer than the Radeon HD 5870 card so it is probably around 12" long. You can expect 2 versions; Radeon HD 5870 X2 and HD 5850 X2 (marketing names yet to be confirmed). From the CCC, you can see that the card in the machine is clocked at 725MHz core and 1GHz memory and comes with 1GB GDDR5 memories so probably this is the 5850 X2 version. Note that AMD is still finalizing on the clocks and other details so nothing is confirmed at this point of time.