Two (unfortunately really, really, really short) clips with hidden nudity. These are less than 5 seconds each.
1) From the Doctor Who episode Gridlock, the Doctor is passing through some vehicles and passes through one with two nudists.
2) From "If Looks Could Kill" (IMDB:
http://www.imdb.com/title/tt0102095/), looking through x-ray glasses.
I was originally going to post these later in the week, but since they're such short clips I decided to post them now. Unfortunately, this means it may be longer before I post in this thread again.
Coming up next: I have nothing at the moment, but I'm working hard at finding something.