Create a new account with Sharebuilder and receive $25. Fine print:
The $25 offer is valid only for new joint, individual and custodial accounts with ShareBuilder Securities Corporation. Not valid for IRA or ESA accounts. Offer available to U.S. Residents only. The $25 account bonus will be applied to your account within 4-6 weeks after your first transaction. There is no fee to set this up; Sharebuilder accounts are free. Win-win.
I've been trading with Sharebuilder for nearly four years now. I have a few hundred dollars deducted from my checking account automatically each month, and it is automatically invested in up to 12 different securities for just $12/month. They have other investing plans available as well, and you can change or cancel your plan whenever you like.