NZXT make fairly good cases. The Lexa is certainly a nice looking case but its not worth the money.
The antec 900 is a bit cramped inside and if anything, go with the newer antec 900 two which has improved on things the original one lacked.
The new standard for gaming cases are the Cooler Master HAF series. The HAF 922 which is a mid-tower has the best airflow when coupled with the side panel fans. Its also fairly roomy for a mid-tower and is top quality. I have the HAF 932 and i love it, i would definitly recommend the HAF 922.
The NZXT tempest used to be the airflow king. That is also a fairly good case but some say that it isn't of the best quality. Its big though and is e-ATX certified and will probably fit all GPU cards