I have used <a href="<a href="http://www.capify.org/" rel="nofollow">http://www.capify.org/</a>">capistrano</a> to deploy both php and rails applications, it works with merb, and probably camping and rack.<p>You need it check into some sort of SCM, then setup some ssh keys and put in your server settings. Then you can deploy it out.<p>It does take a little getting use to, but it helps greatly once you set it up correctly. It's a build and push to server sort of setup. It's great.<p>On the python front, i wouldn't know, but the newer capistrano seems more open to different types of code-bases.<p>If capistrano doesn't suit you, you can always build up some nice rake tasks that automate it for you.<p>just my thoughts :)
PHP has Phing, which is based off of Ant (from the Java world).<p>For Ruby, there's Rakefiles and Capistrano for web app projects. There's also Vlad the Deployer which is more lightweight. For Rails, there's a continuous integration plugin which you could use to monitor your unit tests.<p>If it's not a large project, you might consider just writing your own tasks to automate the process (ssh'in and svn up or hg pull/up). But if you need the ability to rollback or to make sure all your unit tests pass first, go for Capistrano or Vlad.<p>People have used Capistrano for Python web apps too.
Cal Henderson gave a pretty good talk at FOWA Miami that involved some talk about how Flickr does their deployment, you can listen to the mp3 here: <a href="http://cdn4.libsyn.com/carsonsystems/Cal_Henderson.mp3" rel="nofollow">http://cdn4.libsyn.com/carsonsystems/Cal_Henderson.mp3</a><p>deployment stuff is about 3/4 of the way through if i remember correctly.