There are now several launchers available for Android, all of which are heavily customisable with functionality and design tweaks. The launcher that I currently use is GO Launcher EX, which has a huge range of themes available that apply a customisation to the background and icon design. The latest theme that I have installed is Flat Icons, by Mitch S. Flat Icons removes shadows, gradients and reflections from your icons to give them a minimalist look. Not all app icons currently have a Flat Icon design, but the developer does take requests and has a list of icons that are currently under development. The Flat Icons theme is also available for free for ADW launcher, but if you like the theme after installing it, consider purchasing the donate version to help out the developer.
The full list of icons is available to download here as a .zip package should you wish to use them with another launcher.