I use Ameritrade too. You can open an account for minimal money (like $500).
Commissions at Ameritrade are also some of the most competitive. You can enter both market and limit orders for $10.99 per trade up to like 100,000 shares.
I have never had an issue with them in the 3 years I have been trading with them.
I highly doubt you will find any stock-brokerages that will accept PayPal as a form of payment.
Happy speculating.
-Bob