I use sharebuilder. And also E*Trade. I recommend E*Trade.
Forget about the fees. You might save a few bucks somewhere else, but E*Trade gives you an ATM card and then REIMBURSES ALL ATM FEES. That's right. Even a fucking $6 surcharge at a Las Vegas ATM or an $8 one on a cruise ship. Badass.
IB.
Its all about the API...
^^ This, if you are a serious trader. http://www.interactivebrokers.com/
Actually if you're a serious trader:
Any platform with off the chart trading & level II access is good enough.
wells fargo pma = free trades
Their banking kicks ass. I know I have saved at least a grand in ATM fees using them.