Most receivers follow that 19" form factor, the only slim-lines I can think of are the Marantz already mentioned, and the Sherwood 904, which I've heard some negative things about.
What you might consider, if you haven't selected speakers, is an HTIB. Some of the Sony set-ups have very compact "receivers" (less features than a conventional AVR too), and some of the set-ups from other manufacturers (and Sony as well) have built-in disc players and whatnot, which may further reduce the footprint. Finally, Logitech used to (still does, probably; Z-5500) make a 5.1 speaker system that had a "receiver" about the size of a soda can, and it was remote controlled. Far less features than something like the Yamaha or Marantz, but compact and probably very suitable for a bedroom.