VTrader Group LLC, the proprietary trading co., has a customer brokerage called VTFutures. Their rate for mini S&P (for example) is $3.90 round turn plus $500/mo for execution software (choice of X_Trader, Ffastfill, GL Trade) both fees are lower with volume. For those who do NOT want to pay a monthly fee for software, they offer $4.90 RT for J-Trader and $5.40 for Strategy Runner with all fees included.
Best of all they have a dedicated and experienced support staff, and their fees are all posted online.
http://www.vtradergroup.com/VTFutures
Proprietary trading, equities, and discounted eSignal charting for customers are also available