Oooh, finally, a thread for me!
Titanaboa - aka Big Fucking Snake & vore fetishist's dream animal. About 40-50 ft long and 2500 lbs.
Giant ground sloth - Basically a huge sloth. I think if this thing lumbered towards me, no matter how slowly, I'd shit my pants.
Megalania - Take a komodo dragon - an already intimidating animal - and make it twice as large. That's basically it.
BONUS: The Kurī, a breed of Polynesian dog bred for food. Only putting it here because one of the few taxidermied specimens is ugly as fuck and makes me giggle when I look at it.