I actually don't have any sleeper hits yet. But that stuff takes some time for me. For example, The Fugitive was a throw-away from FOTD for a while, now it's a song I listen to regularly. The same goes for Judgement of Heaven. After listening to TXF for weeks I didn't really care for the song - it's not mentioned among my favourites in the "general album ratings" thread, but now it is.
It seems I have one of those on many albums. On DoD it is (wait for it) Gates of Tomorrow, on AMOLAD it is The Legacy. Not that I didn't like The Legacy from the start, but it wouldn't be in my top half from that album. Now it is the song I listen to most frequently from AMOLAD (besides Brighter Than A Thousand Suns).