Which web servers and frameworks work well on the RP? Are there tweaks which can be made to the web server config files that will make it run better given the limited RAM?
There won't be a universal answer to this as there are too many different requirements from web servers for different applications. Questions that will get more refined answers will be along the lines of: I want to host a small Ruby on Rails application on the Pi (instructions at: RPi Ruby on Rails).
The Pi will be able to host most web servers and/or frameworks as both try to keep their memory requirements minimal so that they can support more end users with less server resources. Web servers designed to push the lower bounds of server resources would be useful if the maximum number of clients is desired, trying checking out many of the options listed in Wikipedia's comparison chart of lightweight web servers.
For users wanting more full featured web servers the normal suspects like Apache will work well, but you'll want to spend quiet some time tuning all the options to use the minimal options required by the specific application being used.
As already stated, there isn't a single good answer to this question. There are many web frameworks that will run just fine on the Pi. However...
I'm planning to run a Node.js application on my Pi. Installing Node.js on Arch Linux ARM is as easy as
pacman -Sy nodejs. Using Express and Sqlite you should be able to make a pretty snappy web app that has no problem on the Pi.
I agree it's not possible to give a single good answer to this question. However, some time ago I asked myself the same question and I tried with nginx on the Pi.
I wrote a very simple tutorial on how to install it. Here it is: http://www.joscandreu.com/post/22439909883/install-nginx-on-raspberrypi
I also tried with node.js, however as I wasn't running arch linux but Debian I had to compile node from source with some config hacks, which took around 1 hour. This is the tutorial that worked for me for installing node: http://blog.tomg.co/post/21322413373/how-to-install-node-js-on-your-raspberry-pi