Well I can help you out as I have done lots of research on fuel efficient SUV's, as I am looking to buy as well.
For example, my mom drives a 2009 Nissan Rogue AWD and gets 35 mpg+ on the highway....cost her $17 to make a 3 hr trip the other day!!!! It is a smaller style SUV but that's what makes it so darn good on fuel. I drive a 2008 Dodge Caliber car and it's a piece of crap on fuel...makes me so angry that I don't have AWD and I have a smaller engine, yet my mom gets twice the fuel mileage I do. My advice is to stay away from the non import SUV's if you want fuel efficiency (exception being the Ford Escape Hybrid). Like someone said, a Toyota Rav4 is good, I've also heard the new 2010 Hyundai Santa Fe's are good too as well as the Subaru's. I have a friend that drives a Dodge Nitro, another friend that drives a GMC Torrent, my step mom drives a Ford Edge and I had a Olds Bravada before my car and they are very nice vehicles and ride smooth, but all them are hard on fuel...if anyone says different, they've obviously never drove an import before and can't compare...it's fact the imports are designed for their fuel efficiency. In saying this tho, most these imports I'm talking about are considered "crossovers" so they are a bit smaller. If you want something bigger like a Dodge Durango, then be expected to pay about the same as you would for a half ton truck in gas.
Hope this helps!!!!