An additional six methods, other than searching for radio signals, that may lead to the discovery of intelligent life beyond the solar system.
They are all in the long-shot category though, but some of the possible indications of alien life elsewhere in the universe make for interesting reading:
A civilisation could head off disaster by finding [...]

The people at Search for Extraterrestrial Intelligence (SETI) are once again considering whether to break the so-called great silence, and start transmitting messages from Earth to the stars, in the hope of making contact with an extraterrestrial civilisation.
There is another possibility, says Douglas Vakoch, head of the Interstellar Message Composition programme at the SETI [...]

As pondered by Italian physicist Enrico Fermi. With over 70 sextillion stars in the visible universe, a fair number of which would have planetary systems, why hasn’t even the slightest indication of intelligent life beyond Earth ever been detected?
Fermi reasoned, if there are other advanced extraterrestrial civilizations, then why is there no evidence of [...]

What might intelligent aliens look like? The consensus among experts suggests it would be safe to bet they will not look the least bit humanoid.
Of all the vertebrates, only mammals evolved brains big enough for higher intelligence. And of the 24 orders of mammals only one – ours, the primates – has technological intelligence. [...]

Former astronaut Dr Franklin Chang-Diaz has developed plans for a plasma rocket engine that could drastically reduce travel time around the solar system when compared to the rocket engines currently in use.
But once we have this capability, Mars isn’t really the only place that we can go. With a megawatt-class VASIMR, basically we will [...]

If you’d like to send a 160 character message to Gliese 581d – an exoplanet 20 light years from Earth that is believed to harbour water, and therefore potentially life – you have until Monday 24 August 2009 to be involved.
The signal will reach the solar system of Gliese 581 (the parent star) around December [...]

I didn’t know there were “no life on Mars” conspiracy theories, but it seems there are religious scientists intent on hiding the “truth” from us…
So, the question remains: have attempts to explore Mars been secretly scuppered by religious scientists keen to keep planet Earth “special”? Have they been hiding their sabotage under a veil of [...]

There needs to be careful consideration given to responding to any message received from extraterrestrial aliens, as their civilisations are likely to be far more advanced than ours, says Jill Tarter of SETI.
Tarter acknowledged that there is plenty of reason to be cautious about replying to an alien signal. “We’re in an asymmetric position,” she [...]

Concerns that messages and images being carried aboard the deep-space probes Pioneer and Voyager do not present a “warts and all” view of humanity and life on Earth, have been raised by of Doug Vakoch the SETI (Search for Extra-Terrestrial Intelligence) Institute.
However, a comprehensive message to the stars should not shrink from the details. Might [...]

We were ever to encounter an extraterrestrial civilisation it is unlikely that we would be able to communicate with them by way of the spoken word, something many science fiction movies would have us believe is possible.
Rather we will most likely find ourselves exchanging ideas and thoughts by way of mathematics, says British Astronomer [...]