Old sci-fi movies (with aliens)?

Hi there I'd like to ask you some advice, can you suggest me some titles of old sci-fi movies with aliens?

Even (or rather, expecially) B-movies XD expecially if the aliens are very odd-looking and/or striking (they don't have to be "realistic" or very well-made.)

The thing is, my halloween costume this year will be alien-themed, and while I do already have some ideas I like, I'd like to reference and find new ideas from some of those old movies, expecially for things like weapons and clothing.