stack of the future: trello
This article from Fog Creek Software describes the development stack they used to create Trello. You can summarize it like this: Javascript.
Future is Now
I think this represents something that will become more and more common. Javascript throughout, or at least a lot of client-side work with Javascript and HTML5. Look, Gmail has been around how long? It's a Javascript based app, and most people I know love it. I certainly do. If you've been developing more than a few years, you'd never have guessed things like Google Docs or Trello would have been possible even just 8 years ago.
Oh MongoDB
I think I may have mentioned before how much I like MongoDB. It's a nice balance of features, and more of the middle-ground in the NoSQL field. The only others I can think of similar, are (formerly) CouchDB and RavenDB. Plenty of MongoDB info out there; read Karl Sequin for a good source on MongoDB.
Really Redis
I really need to try Redis; seems to address a good space in the NoSQL world. Session info, message queing, maybe caching if you want an alternative to MemCache.
Don't Doubt Me
Ok, that's a little strong but think about it. Javascript is a language you can use both on the client and server, has good support on desktop and mobile devices, and has a wide variety of great libraries. Plus there's CoffeeScript.
I think Javascript, along with HTML5, is going to be a part of a lot of cool software soon and for a while. I've been thinking about what a good web stack might look like in the coming years. I'd say Trello has a lot of that. I might also look at Ruby or Python on the server, and - yes - C# still too. Although, I think Mono will be interesting too, because with it you can build apps to run on linux, Mac, iPhone, and Android in addition to Windows. The future of programming looks really fun!