I just noticed that discount stock brokerage Sharebuilder is offering a $50 cash bonus as long as you open a new account with $50 by December 31st with promotion code 50WS10. (The code is also mentioned on the promo page.) It doesn’t appear that you even need to make a trade. Fine print:
** You must open a new account with ShareBuilder and deposit $50 or more to be eligible for this promotion. Initial deposit must be completed by 12/31/2010. ShareBuilder will deposit a $50 bonus approximately 4-6 weeks after your first $50 deposit. The $50 bonus offer is available for Individual, Joint and Custodial accounts only. Offer not valid for IRAs or ESAs. The $50 bonus from ShareBuilder is not available for withdrawal for 90 days after it is awarded to your account. This offer is not valid with any other offers and is non-transferrable. Limit one ShareBuilder account bonus per unique customer or custodial beneficiary. [...] Offer expires 12/31/2010.
If you open it quickly, you should be able to take combine this with these several promotional codes worth over a hundred dollars in free trades, both real-time and automatic. Automatic trades differ from the real-time market/limit trades that most brokerages offer, as they are market orders that only execute in batches once a week on Tuesdays. In most cases, this is best suited for people regularly investing a constant amount (i.e. $50 a month) into ETFs or widely-traded stocks. The commissions start at $4 for each automatic trade, and $9.95 for a real-time trade.