AlternativeTo offers social software recommendations
Categories for Windows, Mac, Linux, and Web-based applications are listed. On each platform page, there are tabbed listings for recent additions, most viewed, and most liked software (I'll skip "OMG FAIL", since you're likely not looking for a "worse alternative" anyway). You'll find all the usual suspects listed, like Photoshop, Nero, Word, as well as user-recommended replacements.
Found a specific user whose suggestions you find particularly useful? Click onto their profile page to view all their likes on one page. Alternative.To also taps into Twitter's massive userbase to give you quick access to additional off-site comments about a particular app.
To cast votes or suggest software, you'll need to log in. Fortunately, Alternative.To supports both Facebook and OpenID sign-ins so you likely won't have to sign up for yet another account. The community is still fairly new, so some entries don't have a lot of votes or recommendations yet, but that will change, obviously, as more users participate.