For many people, it's kind of pointless to go searching for a Dock replacement. The Dock itself is one of the most attractive features of OS X and is actually one of the things that lured me into adopting Macs at home seven years ago. But when you have a smaller screen to work with, especially on a MacBook Air, space is a premium. This is where programs such as Tab Launcher come in.
Currently on sale for US$.99, Tab Launcher organizes any type of file on a Mac into a tabbed group, then anchors that group to the side of the monitor. There's a number of options available, such as changing the tab's size, color, font and more. You can even tweak the individual icons on TabLauncher. Like the Dock, you can set it to auto-hide as well.
If you want to switch away from using the Dock entirely, you can import the contents of the Dock to a new tab in Tab Launcher. You can save your Tab Launcher settings and load them on another computer, useful if you have more than one Mac in your household.
Tab Launcher is stable, highly customizable and useful. If you're keen about organizing icons into groups and getting them out of the way to increase your productivity, it's worth dropping the 99 cents to see if this fits your Mac. I wasn't sure at first glance if it would be for me, but so far, it definitely is.