"Popular" here is going to mean maybe 15% market share, if my memory serves correctly. Popular server languages remain Java, PHP, ASP.NET, and increasingly Ruby.
In my mind, the reality is that you should choose the programming language based on the skills of you or your programmer(s) and the task at hand. If I were going to implement a banking system, I'd probably look first at Java and its J2EE libraries to see what options were available there. I've used PHP recently (despite it being a reasonably painful language) because it has some wonderful productivity and scalability features that we've been able to really take advantage of.
However, I've nothing against any of the other platforms (with the exception of a slight bias away from anything that requires me running windows servers), and have been fiddling with Ruby, and also exploring Haskell, Erland, Clojure, and even Scala.
Unless we're talking in-house applications using VB or C#, or mobile phone applications using ObjC or Java, "client-side" almost always means HTML/CSS/JS these days.
So, look at the task and the talent, and go from there. Most of the common platforms that you've heard of are all going to have large enough communities for support and libraries to perform various non-standard tasks.
Good luck!