Two of my favourites are Mourning Dove and White-winged Dove (see picture above). Like the Rock Pigeons, these two are pretty common sights in urban Tucson. In some ways, I think they're pretty similar: as evidenced by my photo, they choose the same perches, in posture they are both fairly upright and they both have tails that extend far below the wing tips. Of course, there is the obvious size difference, very obligingly projected by these two birds as they perched next to one another, as well as the clear white wing patches which provide a nice white edge when the White-winged Dove has its wings folded. But sometimes, you don't get two birds together nor do you get a profile view.
If you're lucky enough to hear the bird you'll easily be able to distinguish the Mourning Dove's slower, really melancholic song from the White-winged's owl-like call. But what works for me every time is looking more closely at the tail: while both birds have long tails, the Mourning Dove's tail is sharply pointed, a characteristic you can see from any angle. In contrast, the White-winged Dove's tail is really quite blocky. If you glimpse the tail from underneath you'll of course also see the dark tail band. Either bird is really quite beautiful--as are Rock Pigeons--and deserves some appreciation. All three of these birds are shot in the States, but I prefer to shoot them with the camera.