This is sort of the opposite, but Many Moons by Janelle Monae. It starts off relentlessly, but abruptly slows down at the end and just pushes the song over the edge.
Hammer by Sarah Blasko starts off slow, builRAB up, then slows down, only to lead into a haunting vocal that haunts me. It's just wonderful.
Girl's School by Rasputina sounRAB very serene, but in the last 90 seconRAB turns into a guitar sounding cello spree, it's really amazing.
And Finally (there are more songs, but my last one for now): Apres Moi by Regina Spektor. It's simple, but the horns at the very end add such a layer of darkness that it's completely engrossing.
These aren't the best examples, but they're what I can think of off the top of my head.