For some people big just isn't big enough ! I would've never imagined seeing some of those things in the hobby 
Arapaima gigas:
http://www.youtube.com/watch?v=kFOPoN-zMRA
Semicossyphus reticulatus:
http://www.youtube.com/watch?v=5b2O01gm8LI&feature=related
Ginglymostoma cirratum:
http://www.youtube.com/watch?v=iRZcSCxonDg
Epinephelus lanceolatus:
http://www.youtube.com/watch?v=FKdLYS4N4ms
Pristis microdon:
http://www.monsterfishkeepers.com/forums/showthread.php?t=756
Feel free to go on !

Arapaima gigas:
http://www.youtube.com/watch?v=kFOPoN-zMRA
Semicossyphus reticulatus:
http://www.youtube.com/watch?v=5b2O01gm8LI&feature=related
Ginglymostoma cirratum:
http://www.youtube.com/watch?v=iRZcSCxonDg
Epinephelus lanceolatus:
http://www.youtube.com/watch?v=FKdLYS4N4ms
Pristis microdon:
http://www.monsterfishkeepers.com/forums/showthread.php?t=756
Feel free to go on !