Thanks Cetacea for the clarification that Delta offer is also for existing customers. I didn't realize that before (I already have received AA miles).
I also noticed that the offer of 25,000 Membership rewards points for $50,000 deposit was extended to 9/30/2011:
Open and fund a non-retirement Fidelity brokerage account today and you can earn up to 25,000 Membership Rewards points. Offer valid for new customers only.
https://scs.fidelity.com/other/offer...shtml?MSC=AX01