You can earn cash back via secondary market travel sites like Priceline, Expedia, Orbitz and Hotwire when you click the link from Ebates. This is best for hotels and rental cars.
Ebates isn't just for "big box" online retailers. Ebates is similar to airline shopping portals except you get cash back (instead of miles) by clicking the link. Generally it is better to buy flights via the primary market (unless you find a crazy deal on these sites) but you can find great hotel and rental car deals on sites below, especially with a "name your price" feature. If you find a great hotel or rental car deal via Expedia, Hotwire, Priceline, etc... see if you can get cash-back for something you were already booking. Just click the link through ebates to get additional cash-back.