Beholder 20
Displacer Beast 20
Drow 16
Flumph 20
Gelatinous Cube 21
Githyanki 20
Gnoll 20
Lich 20
Mimic 20
Mind Flayer/Illithid 20
Owlbear 21
Purple Worm 20
Rust Monster 20
Tarrasque 20
Umber Hulk 20
Gelatinous Cube is one of those monsters every adventurer meets early in their career, so it gets my first vore. Its downside to being iconic is that it sure doesn't lend itself to inspired artwork (unlike, say, the owlbear), unless one can draw something cool floating around in it (like, say, maybe an owlbear).