There are two answers to this. First, the song I, along with everyone else, cannot escape this summer, is Foster the People's "Pumped Up Kicks." Now, it's an interesting song, but I haven't fallen in love with it. I don't hate it, either. I'm simply ambivalent. Of note: On VH1, when they show the video, they bleep up the words "gun" and "bullets." As my 15-year-old son says, it makes it seems even more bizarre than it is. And it's pretty messed up.
The song I hear on the radio all the time that is the most surprising, however, is "Blister in the Sun," by the Violent Femmes. It was never on the radio when it first came out, at least not in middle America or off the college radio stations. Now, I think I hear it at least once a day. If it's not "Blister," I hear their "Kiss Off," which I like better, as I'm personally less sensitive to drug references than to "big hands" ones.