Full Tower
CM HAF 922 Full Tower = $150
Antec P183 (Upgraded P192) = $150
Mid Towers
CM Storm Scout = $100
Nzxt Beta or Beta Evo (for the cost effective option) = $40 or $50 respectively
+1 on both the CM HAF 922 and Antec P183.
I was also looking at buying a case (my thread should be just below this...) and I eventually chose the HAF 922. It is a mid tower (extreme side of midtower range...) and can fit 2x5870s with room to spare (same size or a bit bigger then a GTX 260?). It is also very moddable if you want to go down that line, can fit many fans and also has the room to fit very large aftermarket coolers.
My other choices on cases were the Raven RV 01, Antec P183 and the Lian Li Lancool PC-K62, all of which should be in your budget. The Raven RV 01 is very large and has a unique feature in which the motherboard is on a 90 degree turn so your IO Shield is on the top. This gives better airflow for the case and it also gives more room for GPU cards. 5970's can fit easily which are the largest cards on the market atm. However cable management is a little hard (as most full tower cases are...).
The Antec P183 is a sound proof case. It uses three layers (aluminium, plastic?, aluminium) to absorb sound so you don't hear the fans running at full thrust. It has fairly decent cooling and overall is a nice case.
The Lian Li Lancool PC-K62 is a very nice mid tower case that offers many of the features lots of the more expensive cases have. It has a great black interior with one of the best tool-less designs around and decent space to fit a 5850 with a 5870 just squeezing in. It also goes with the Blue colour scheme and so its fitted with 3 Blue LED fans (120mm?) to cool the case fairly adequately. Overall a good mid tower case.
Another case you could choose could be the HAF 932 or Storm Sniper. I think both look fairly ugly but they are the best full tower cooling cases around. If you really need a full tower case then choose one of those. Also if your computer shop has any in stock, the CM 690 II Advanced is a new case that seems to be fairly good for its price tag. Maybe pick one of those up?
Its really up to you. All these cases are fairly unique in there own way and would all suit you fine. Hope you find the case your looking for.