In Superman Vol. 2 #74 (part of the Death of Superman storyarc), the Justice League faces off against Doomsday. Now, this is the villain that will kill Superman, so needless to say the League get their butts handed to them.
Poor Booster Gold in particular got pretty beaten up. Doomday even destroyed his suit, which is a big deal considering he has no superpowers and relies in his costume to fight (its basically a skin tight Iron Man suit). Another reason it's a big deal (for me anyway) is because we get some Booster beefcake. Love 'em hairy nipples!