In Q3, July to September, the 5% promotional cash back categories are :
Chase Freedom:gas stations and more
Discover :Home Improvement Stores, Department Stores and Amazon.com
Citibank Dividend : airlines and Hilton hotel properties
Some pretty good categories there. Gas stations at Chase and Amazon from Discover both give lots of opportunity to get 5% back. Airlines could be worth a good amount if you're planning any air travel but you'd have to book direct with the airline.