Depending on the area (and your stomach),
www.rewardsnetwork.com sometimes includes national fastfood chains, but this is usually a rarity. Examples I have found are Sonics in the Columbia, SC area and Steak & Shake & Denny's in the DFW area, Denny's, Jersey Mikes & Burger King in the L.A. area. Each quarter, different airlines offers bonuses through rewardsnetwork. Currently Delta has a 500 mile bonus for each $50 spent on restaurants in the program, on top of the 5 miles per dollar spent (if you are at the highest level). Last quarter AA offered the same deal, up to a total of 5000 miles. However their current bonus for the 4th quarter is only a "plus 2" or 7 miles (highest level) per dollar charged.
If you like Sweet Tomatoes, I have found the best deal would be the discount coupons they offer in the Sunday ads, about once a month. Lately they have been including a BOGO with their coupons. I also use or have coupons for Longhorn, Mimi's, Olive Garden, Red Lobster, Perkins, Jersey Mikes, again all from the Sunday ads.
Although Mrs. Outoftown and I have been to all of the above, we have also used $10 & $25 GCs obtained for coke points from mycokerewards.com for Subway and Panera Bread, since they quit offering Delta miles and Hilton Points. See the SPAM forum for more info on this.
Personally, I like to quadruple dip by combining a coupon + rewardsnetwork miles + stamps for free food + AMEX Costco, which has a 3% rebate reward for restaurant charges. In my area (RDU), Sunset Grill restaurants meets this criteria, so they are naturally our favorite restaurant.
HTH,
-outoftown