Mr G's is OK, and truly Yuman, but not what I would recommend. It tastes great for those who grew up in Yuma, but the food is very lardy and often not real appealing to those unfamiliar with it.
Los Manjares de Pepe, 2187 W. 8th St, is probably the best restaurant in town, and very affordable:
Lunch specials are always good, plus I would add Pepe's special tomatillo pork and also the sinaloa chicken as good dishes in addition to ones discussed at the blog.
re: Ed Dibble
I should add that with the construction at the 16th St exit, the best way to Pepe's would be to exit at 4th Ave, head into town, take 1st St (the first turn) to Ave A, take A to 8th St, then head west on 8th until you get to Los Manjares. It'll be on the left about 3/4 of a mile west of A.
Yuma is home to tons of wonderful mexican food restaurants. There is one place that stands alone as the local staple and favorite, Mr. G's. Owned by the gutierrez family who also own Chili Pepper (mr.g's sister restaurant) and La Casa Gutierrez (their sit down place). I would recommend The green or red mix burrito, The bean and cheese is also great (the beans are made with the grease they fry their rolled tacos in). The rooled tacos themselves are the best I've ever found. The salsa is the perfect compliment to all of their food. I think you will agree that the salsa is distinct and unlike anything you will find elsewhere. You can't leave with out buying a bag of their homemade paper thin tortillas which are made fresh daily (if they have any left, they go quick). Having grow up there and frequently coming back to visit family, a weekend is not complete without a lunch at Mr. g's. Closed sundays, enjoy!