If you haven't seen this visualization of space yet, you should. Click here for the large version -- don't look at the thumbnail. Even though stuff like this gets posted on the internet all the time, it continues to blow my mind. So if you've seen it already, let me remind you again of how insignificant you are. ;-)
The interesting part of about this picture is that it is billions of years old. The age of the universe is more than 13 billion years, but due to the expansion of space we are observing objects that are now considerably farther away. According to this Wikipedia article, the edge of the observable universe is now located about 46.5 billion light-years away. A lot might have changed in 13 billion years.
In other words, you better believe there are aliens out there.
Or as Douglas Adams put it in The Hitchhiker's Guide to the Galaxy: "Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it is a long way down the road to the chemist's, but that is just peanuts to space."