No, SETI hasn't found any yet.
I've already talked about why and how to search for alien life. Now to speculate about what non-terrestrial life would be like. This is somewhat topical because in a week there's a National Geographic channel program showing off their ideas of what alien life might be like.
There are two main schools of thought about alien life.
The first is the "as we know it" school. Life is defined as something kinda like what's around us on Earth -- based on strings of nucleotides, made of proteins, and using water as a solvent. This is the default school for most serious scientific programs to look for life beyond Earth. When we send probes to Mars, they're looking for liquid water, carbon compounds, and signs of biochemical activity. It may be unimaginative, but it does have some advantages.
As-we-know-it life is also easy to look for. Since we know the range of environments where it can thrive, it narrows the focus of any search immensely. No point in searching Mercury or Venus because there's no liquid water and never has been. No point in looking on Pluto. Before the 1980s we would have said there's no point in looking among Jupiter's moons, but then some bright boys at JPL noticed that Europa might have a subsurface ocean, which meant that a formerly obscure moon became number 3 with a bullet on the list of Places to Search For Life (Earth holds the number 1 spot permanently, Mars is still hanging on to number 2 by its red-caked fingernails). On the interstellar scale looking for life as-we-know-it means a relatively small class of stars (main-sequence F, G, and K stars, mostly).
Moreover, we know for sure that as-we-know-it life is possible. After all, we're here, right? All other forms of life are conjectural. If you're spending billions on a space probe, conjecture is a very dodgy thing. Sure, there might be plenty of ways life can exist, but it's hard to build a probe capable of searching for all of them. And if you have to pick one kind, why not the one you're certain is possible?
The big problem with the as-we-know-it school of thought is that so far it has produced only one hit: Earth itself. We haven't found any unambiguous traces of life elsewhere in the Solar System, and we haven't identified potential lifebearing worlds in any other star systems. So maybe we shouldn't be looking for life as we know it after all.
The second school of thought might be called the "anything goes" view of alien life. Life is any self-organizing, self-perpetuating process which can evolve greater complexity. DNA-and-protein-in-water is just one in a whole universe of possibilities. Anything which can act as a method of information storage and self-replication can be the basis for a kind life.
This means you can have life based on magnetic field loops on the surface of stars. Or chains of fluorosilicone molecules in seas of liquid sulfur. Or complex hydrocarbons in methane. Or metallic hydrogen at the core of a gas giant. Or superfluid helium on an icy world like Pluto. Or ionized dust grains in an insterstellar nebula.
And these are just the ones scientists have imagined. Science fiction writers have come up with even more exotic possible life forms, including Douglas Adams's "superintelligent shade of the color blue."
The chief problem with all these not-as-we-know-it forms of life is that it might be very hard for humans to even recognize them as living systems. When can you say something is really alive, as opposed to being just a complex chemical reaction in the local environment?
This isn't an easy question. My house's septic tank needed replacing a couple of years ago because of a kind of "rot" breaking down the concrete it was made of. Basically, a complicated chemical reaction involving the waste products from the water-softening system tended to attack the concrete. It acted for all the world like some kind of "life" digesting the concrete, like microorganisms breaking down a carcass. Was the concrete rot alive?
You could say it was just a chemical reaction, and once deprived of its source chemicals it would stop. Of course, we depend on chemical reactions to live, and if deprived of, say, oxygen, we'd stop, too. Are we alive?
Complexity seems to be the key. Stop a living system's chemical reactions and you can't start them again. Living things die. And living things are born: you can't make them just by tossing together the right ingredients. Living things expend energy to maintain and increase their complexity.
In the Solar System this means we might miss entire ecosystems simply because they don't look alive to us. Some scientists have started looking for suspicious chemical imbalances (like Earth's oxygen atmosphere). Any situation which would normally be temporary, but is somehow being maintained, is at least a suggestion of life.
Over interstellar distances, this isn't so much a problem. While there are plans to search for potential lifebearing worlds in nearby star systems using large optical interferometers, most of the search for life beyond the Solar System must be aimed at technological civilizations. We're listening for other people who can make radio transmitters. This ignores planets teeming with as-we-know-it life and worlds populated by bizarre not-as-we-know-it forms equally.
As a completely subjective matter, I come down on the side of the not-as-we-know-it school. I expect that when we do find life beyond Earth -- and I do expect it -- we will discover that it is, in the words of J.B.S. Haldane, "not only queerer than we imagine, but queerer than we can imagine."