GNI Touch are pretty good
Not sure about Velocity Futures but a lot of members here use Tradestation - seems to be the home standard.
Shouldn't be a problem using US brokers, just make sure you know what your rights are and what protections are available if they 'misplace' your money or go busto.
Also, take a look at futures betting, a spreadbet firm with a difference. It may suit your requirements:
FuturesBetting - Financial Spread Betting Homepage