Horses falling out of the sky never fails to make me smile, although it happens quite a bit. Also, weapons and shields drifting verrrry slooowwly up into the sky.
Once in a while I get attacked by a generic, invisible male khajiit. Always a male khajiit, always completely invisible. Don't know what causes this—could be a mod conflict somewhere, but I haven't been able to narrow it down. It doesn't happen often enough to be a major concern, although it's pretty distressing when it does happen.
Then there was the time I walked into Jorrvaskr and talked to Skjor. The thing is, he should have been dead. At that point my wife, Borgakh, started walking backwards around the table in the main hall very slowly, which should have been an indication to get the hell out of there. But no, just to see what would happen, I accepted a quest from not-entirely-dead Skjor. That did NOT work out well. I got this quest objective arrow that kept teleporting to a different place each time I looked at the map.