I don't believe in Ghosts, as in "spirits of dead people hanging around", but I do believe its possible that something lives that we can't usually(or ever) see.
Aliens I totally believe in, but haven't seen any. I wouldn't mind at all. I have had a strange experience that could be attributed to abduction--for years when I a teenager, I would go to sleep and wake up with short scars near joints in my body, like old wounds(ones I would certainly remember) that have totally healed, but in a way that my cuts never heal. Always in a similar pattern too. Never figured it out, they are all still there.