The only evidence we have at this point is statistical. The model for life is us, so we've used our location (in relation to our star) and our necessary elements for survival (like water) as the basis for our search. We've already discovered many planets in the "goldilocks" zone and soon, we should be able to detect if they have life sustaining elements on their surface.
So, as of right now, there is no concrete evidence. But the statistical evidence is pretty compelling. Considering how many stars there are in the sky (and galaxies in the universe) it would be unlikely that we are alone. And I suspect that we will have our answer fairly soon (within the next 20-30 years). While that discovery probably won't be little green men (more like little green microbes) it will be no less significant.