Dock Spaces is a really cool app. It lets you customise a series of Docks which you can then tie in with Spaces (comes built into Snow Leopard) and in return you can have a customised dock for every space you have set up.
For example I have a General/Web space and the apps on my Dock include Mail, Web Browsers, and Social Media tools.
The next space is for my Web Design and Maintenance stuff, so all tools to do that clever stuff as well as photo editing and a few utils sit on another dock there.
My next space is for music and media. iTunes and other apps are on my dock there.
My next space is for Office apps.
Anyway, you get the idea. It’s a £5 pound app, for Mac OS X and is guaranteed to be useful if you want to make the most of your Mac or are of the productive kind.
You can find it here: http://www.nscoding.co.uk/