Quite a few of them, depending on the time of day, time of year and your location on Earth at the time! Venus is usually only visible for an hour or so before dawn or after dusk, but it's generally much brighter than the stars and could easily be mistaken for a UFO. Huge Jupiter comes close enough to see with the naked eye on occasion, too. Again, it will probably appear brighter than most of the stars and seem to be impossibly big and bright to say that it's many millions of miles away.