i'd go with Torche, Fu Manchu and Kyuss. all three (but particularly Torche) have those melodic guitar parts that, for me at least, evoke images of heat haze above an asphalt road.
also, i'm not sure how many on here would agree, but i've always found that Less Than Jake's "Hello Rockville" to be perfect summer/hot weather music, and likewise Alkaline Trio's "Good Morning" (in spite of the snow/cold references in the lyrics).