Best Case to fit HD 5870.

The Coolermaster CM690 is a very good case. Ventilation, airflow, and cooling are excellent.

Another case you may want to consider is the LianLi Lancool Dragon Lord. It comes in several models with and without a side panel window:

http://www.lancoolpc.com/en/microsite/01/

Here's a link to a video review by the guys at mnpctech.com:

http://www.youtube.com/watch?v=U2MdUGxWEcU

prices for all models are under $100.00:

http://www.mwave.com/mwave/deepsearch_v3.asp?scriteria=...

CM690, HAF922, HAF932 and Cosmos S!

CM690 is the best bang for the buck!

Cosmos is best in looking with good cooling too, but it's much more expensive than the rest of the cases I mentioned.