Well for client-side it's either Javascript or something that compiles to Javascript, for Server-side quick stuff nowadays I'd recommend Javascript. You can do a lot very quickly using Node.js as a server-side Javascript platform. It's build on Google's V8 and uses Javascript to script creating servers. Did I mention Javascript yet?
This is probably too much for tomorrow, but not a fan of Javascript? I'm not either. But Javascript has basically become the ASM of the web. It's not a particularly good ASM, but somehow there's a sizeable market of compilers to it and even new languages being created specifically to compile to Javascript. Typescript is Microsoft's attempt to add static typing to the language (and I much prefer static to dynamic languages), Coffeescript and LiveScript are both attempts to create a more python-esque language that removes a lot of Javascript's boilerplate...
Heck, for "needlessly complex" there's even Emscripten that can compile C++ to Javascript! With support for turning either SDL 1.2 or OpenGL ES 2 into WebGL calls!
And that can literally allow for 3D games with fairly impressive graphics, for a browser game at least... It's starting to get crazy what can be done in a web browser nowadays...
As an aside, this is pretty cool:
Koding. It's a "Cloud Development Environment". They basically spin up a linux VM for you, open a Javascript-based terminal for that VM, and let you do whatever. When you leave the terminal, they shut down the VM but if you have an account keep the data. The VM they open runs a web-server, so you can use it for websites or for writing more traditional programs.
There's also a non-terminal editor that can access files on the VM, which is based off the same web-based editor as Cloud9 and allows for things like multiple people to edit files and chat. Which is probably useful...personally for Linux coding I just use VIM with a craptonne of plugins, but I'm crazy and isolated like that at the moment.
I find it useful for developing when away from a powerful PC, I use it with my Chromebook to still be able to program. You can even create a guest terminal for free without creating an account, which just spins up a temporary VM for you by going
here.
The monetization model seems to be mostly based around "1 free VM, 1 free GB of storage on that VM" and if you want more you pay. All in all I think it's pretty cool. If anybody wants to sign up for it, I have a referral link (because I'm being a whore for more storage space)
https://koding.com/R/morleydev