Well.... it didn't actually make the UK Top 40 and in a sense it's not that mainstream (they're a rock band, albeit a very commercial one!), but....
Kiss - I Was Made for Lovin' You
I love the song, I actually bought the 7" single at the time, and even though it's only a few seconds long Ace's guitar solo gives me chills every time I hear it, even now. The note choice is perfect and the tone is awesome.
(That's assuming it is Ace playing it! You can never be sure with Kiss.)
Great thread idea, by the way. I just wish I could think of more good replies. :D