I have been using Think or Swim since before TD Ameritrade bought them, and it's pretty great. The charts in my opinion are the best that I've found, highly customizable, and feature rich.
You can trade all types of securities as well. And it's very easy. The mobile app is also top notch.
Depending on OP's needs, this is probably the best. If he's trying to trade, he can open an account and (I believe) there is no minimum balance for buying/selling. I think $3k is the minimum for margin trades (and you get super-low commissions if you fund that much).
But you don't even need an account to use it. Just create a paper-trading account and you have access to the application, plus you can play around with trading without actually spending any real money.
Furthermore, dough.com is (kind of) a branch off of ToS - less functionality, but a much prettier interface. You can sign up on dough and get full access (without being able to actually trade, of course) without a brokerage account or paper account at all.
You can trade all types of securities as well. And it's very easy. The mobile app is also top notch.