Sometimes it does seem rather stupid, but they make up for them once in a while.
Spider-Man - as someone mentioned before, he's wearing that type of a costume for flexibility, and it doesn't look that bad. That's a good example
Batman - when he has the spandex w/codpiece thing going on..that looks ridiculous. But you have to admit, in Batman Begins, that was beyond realistic.
Superman - pointless that he has that costume, he could wear anything, like someone else said. The only reason for having that would be the quick access underneath his clothes, but having those red shorts on top of the spandex, just seems a little odd and unnecessary.
Hulk - how do those pants stay on?
Silver Surfer and others - the "non-costume costume" is something always kind of cool, and realistic...as realistic as you could get for a character that comes from space and whatnot lol
F4 - the movie did a good job with having it believable, and their costumes don't even look bad
Galactus - you'd think a guy as powerful as that, who knows so much...would wear something besides pink..lol They really should redo that costume, make him AT LEAST blue and silver or blue and gold or blue and black or god, anything but pink lol.
Yadda yadda yadda