NES - Magician, Contraforce, Battletoads and Double Dragon, some 260 in 1 cart, Adventure Island 3
SNES - Chrono Trigger CIB (not rare by demand is pretty high vs. supply), Eeak the cat (apparently rare but not valuable)
PS1 - Valkyrie Profile, Lunar 2 Complete with everything, Tomba!
PS2 - Probably Sakura Wars collectors edition
DS - Electroplankton, Also Radiant Historia and Infinite Space (both these aren't really rare but supply can't seem to meet demand)
PSP - lots of collector's editions (all the Ys, Legend of Heroes, Persona 1 & 2)
Saturn - Albert Odeyssey, Shining Force III
Nothing super rare but I've got some decent stuff.
I generally won't spend alot on something rare unless I intend to play it a bunch.