Not sure what an application launcher does? It's basically a tool to organize shortcuts to applications, and some can even disable the appearance of your Start menu and Taskbar.
Below are three launcher programs, each providing a different experience and list of functions but all acting as alternatives to what Windows has to offer.
The first alternative on the list is a small, open-source launcher. Some degree of customization is built into the program in the form of skins and icon packs. While only two skins are available with the installation, several more are available for download from the project's site. Furthermore, being open-source means that if you know how to code (the project is written in C++), you will be able to add additional functionality to the dock. This is still a good, solid launcher even if you have no programming knowledge.
RocketDock is a portable, lightweight, and free launcher. It's great for running on an older, slower system or even a faster system that you don't want to waste CPU cycles on. Several skins come with the installation built-in, and each of them has several options for customization. There's an option to minimize windows to the dock, which is great if you're looking to hide the default Windows taskbar. Vista (and possibly some Windows 7) RocketDock users will also enjoy real-time window previews of minimized programs.
If you really want to customize your computer's interface to the point that it doesn't even look like you're running Windows anymore, ObjectDock (and the rest of the ObjectDesktop suite) will be your favorite tool. This program is available in both a free and paid version, with the free version having enough options available to make it sufficient for a more common user's needs. But if you want the most customization possible, you'll need the paid version. The paid version allows multiple docks, tabbed docks (so you can sort your applications by type), and doesn't restrict docks being on the side of your screen. An option is also available to minimize windows to a dock and display your system tray, completely eliminating the need for the Windows taskbar.
Which dock you choose will depend largely on what level of functionality you require. Try each of the above programs to find which one best fits your needs.