Are we alone? The Arecibo Message
The message was actually transmitted on November 16th 1974 and consisted of 1679 pulses of binary code (0's and 1's) - which took a little under three minutes to transmit. It was transmitted on a frequency of 2380MHz.
And it seems on in August 2001 we might have received a reply in the form of crop circles in Chilbolton, England. The crop circles depicts a slightly altered information sequence in comparison with the orignal message sent.

You can find more information about the original and "received message" here , here and here.
As far as I can gather these crop circles haven't been proved or disproved as a hoax. This provides for some interesting questions. Could this actually be a reply from an ET? Maybe... maybe not...
The question if we are alone to me is a no brainer. Personally I don't believe that we are. There's just too much possibility of live out there. The real question is if/when we will make contact. Perhaps it's already happened and we just don't know it!