Title says it all: She just found out that her husband is Superman.

How long have they been married? What gave the lunkhead away? What implements will she use to disembowel him? Do they have kids?

Is "She" even Lois?

Is "He" even Clark?

There is a Story quite well matching your criteria: "Lois finds out" by Movile Richard.
http://lcfanfic.com/stories/1999/html/loisfind.html
A very funny tale.

You could also check out [begin shameless plug] my story Standup and Be Counted. [/end shameless plug] Their relationship flows along with the action plot, so it may not be what you're looking for. But chapters 12-14 have that revelation in them, and even though it isn't a funny story, there are elements of humor scattered throughout.

Lois Finds Out

Its raining, my chores are done and so I'm going to treat myself to this fic!

Not quite, what you had in mind, but I hope you migh still enjoy...

The Final Excuse

That was fun!