My two 8800GT in SLI run at between 52-55C Idle and around 66-71C at Load stable with overclocks.
1. Use RivaTuner and create fan profiles to cool the GPU as it increases in temp while gaming (all the way to 100% fan usage after hitting 65C).
Go here for a guide and pics on how to do it;
Now other things you can do to reduce GPU heat include;
2. Make sure that you have good air flow in the case and you have good cable management.
3. Make sure that your video card is clean and that the GPU stock fan is free of dust.
4. Remove stock fan, remove factory thermal paste, use good thermal paste like Arctic MX-2 or Tuniq TX-2 and reseat fan.
5. Buy an aftermarket GPU fan like the Thermaltake DuOrb.
6. Mod your case and insert a 120mm fan to exhaust the GPU heat directy out of the case. Refer to my Sig for the Mod instructions.
7. All of the above.