Of the monsters I've covered in the Monster ENCyclopedia series, I don't recall ever using a catoblepas, a flumph, an ixitxachitl, or a peryton.
As far as other creatures go, the tarrasque I've used but only once, as a side encounter leading up to the climax of a campaign, where the goal wasn't to kill it, but simply to avoid getting killed by it on the way to the real villain of the story.
I really like strange creatures, and have used many of them over the years. Still, my best estimate is that there are currently between 9000 and 10000 unique D&D creatures, so even if you are a voracious consumer of unusual creatures, you'd need to run a lot of games to make any kind of dent in the total.