Honestly there are tons of evidence (aside from some random images in the sky) that show aliens have and still do visit us. Take the Dogon tribe in africa. It was discovered that they have ancesteral evidence about star systems, other stars and planets, and even drawings of an alien race that supposedly visited earth and taught them all of this. What stumps scientist, is that the dogons knew about this well before modern science even knew about it all. Basically...
Dogons knew about the siris star system and how our solar systems looks from space, supposedly thousands of year before modern science discovered this.
Do i belive in alien life. Yes i do. Do i belive all of the half-wit, "sightings" that tend to populate youtube these days. Hell no i dont...shit is too dam ridiculous....either way, for those that ever read anything by Drunvalo Melchizedek then you would probably feel the same way....then again, some of the shit he says is just too unbeliveable yet, is somewhat grounded in truth (amazingly)
EDIT: forgot link to dogon ppl....
http://en.wikipedia.org/wiki/Dogon_people
Drunvalo Melchizedek Home page