What sort of monster movies are you looking for? There are a lot of sub-genres even in this like Horror, fantasy, horror-fantasy, sci-fi, sci-fi horror, or simply gargantuan creatures on rampage [very few movies in this category though]. But looking at the choices you mentioned, one would think that you are interested in only rampage movies. So be a little bit more specific so that more suggestions can come in.
If you are interested in all the genres mentioned above, here are some of the best.
Horror - The Howling, The Fly, Fright Night, REC, Demons & any Romero zombie movies
Fantasy Horror - Sleepy Hollow, The Hellraiser series and other Clive Barker adaptations
Sci-Fi - The Thing, The Blob, Slither & the Predator series
Sci-Fi Horror - Event Horizon & Pandorum,
Monster Rampages - Godzilla [Not the Roland Emmerich Crap, but the original Japanese Godzilla] Cloverfield & King Kong