Let's start off with a species that consists of more than one sub-species, a White-crowned Sparrow. Below are photos of the sub-species gambelii and oriantha. Very similar, but also very different once you look at the photos. Check out the striping on the head and also the color of the beaks.
The White-throated Sparrow is a bit similar to the White-crowned and sometimes mixes in with White-crowns and is often overlooked by novice birders.
Next we have a Black-throated Sparrow, a Black-chinned Sparrow, and a Sage Sparrow. The Black-throated is one of my favorite sparrows; handsome little birds! Sage Sparrow is not too bad either!