TD Ameritrade allows you to sign up for free. You can paper-trade on their thinkorswim platform after you've signed up. I think it's a little bit delayed for paper trading if you haven't deposited like 2,000$ and signed a few forms. But they have the best platform in my opinion and it wouldn't hurt to start learning how to use it. They also have free seminars in the chat rooms that teach you invaluable trading tips.