NES: Ufouria is uncommon and highly desirable, Banana Prince was only released in Germany. Mr Gimmick is definitely the rarest PAL nes title and will set you back a few hundred bucks...

SNES: Daze Before Christmas only released in Germany, Castlevania Vampires Kiss seems pretty rare

Megadrive: Daze Before Christmas only released in Australia, Alien Soldier seems desirable but I dont think its actually that rare..