I use my normal futures brokers (UBS, Man). I also use my IB account to trade the Osaka Nikkei contract. Any good global futures broker should have access to both exchanges, but IB only trade the electronic one (Simex is pit-traded). I like the Simex contract because it trades wider hours (I'm based in the UK, and Simex trades up until 12pm my time, so I don't have to stay awake till 7am to react to the closing price in Tokyo!).
You might want to try Refco - I am thinking of opening an account with them, they have a good front-end, cover loads of markets, and have reasonable commissions. I believe waggie has an account and is very happy with them.