Hooksexup once did a Top 5 Funny Sex Scene list. Unfortunately, we disagree with almost all of its choices ("The Graduate" being the only exception.)
Here's a new, much funnier list, with not only great sex scenes but barrels of laughs (we had a hard time imagining anyone would laugh at the raunchy sex in "Havoc.") Barrels of laughs during sex? Can't say we've ever experienced that... no, sir...
5. Animal House.
4. Because couldn't find clips for Being There or Sideways, another equally-worthy scene from Animal House: