I think it's been suggested that if there is intelligent life out there, it would probably be generally similar to us. Certain developments have allowed us to become as advanced as we are - things like opposable thumbs, big brains, bipedalism, vocal chords - helped us get to where we are today. Logic says that any other species out there that is as intelligent as us would have to share some of these characteristics.
Obviously, what they look like depends on what their planet is like, though.