personally, I use xpresstrade for my commodities, and ameritrade for my stocks. I like xpresstrades features.
interactive brokers offers stocks and commodities but it didn't look very attractive to me. I judge books by the cover apparently.
In case you are new at this, there are expensive margin requirements in order to participate in contracts of gold and crude oil. A contract is what you can consider a share but much more leveraged.
I wouldn't suggest you buy commodities, but options on commodities. They lower your risk because you don't owe money if you make a bad trade decision, and it is just as leveraged, but no margin requirements. Commodities are only good if you plan on day trading, as you should never stay in a trade over night.
If you need anymore info, PM me. Or check out my site for some strategies