$65 Paid on my Sharebuilder Account

I made $65 on the Sharebuilder-Costco account promotion today when the promotion amount was credited to my Sharebuilder account. I signed up for the promotion as a Costco Business member and Sharebuilder promised to credit me with $65 once I executed my first trade.

I transferred $100 into my Sharebuilder account and purchased four shares of PBW, the alternative energy Powershares ETF that tracks the WilderHill Clean Energy Index. That trade cost me $15.95 and have since earned back the commission amount since the late March trade.

Sharebuilder was good to their promise, and promptly credited the amount in 4-6 weeks. Now I can either:

1. Let it ride
2. Use the free money to execute more trades; add more funds
3. Set up an ACH transfer @$4 per investment the first Tuesday of the month...

I'm considering the options.