Minecraft Version Changer provides a big list of Minecraft versions to choose from. It takes just seconds to change between versions. You can even generate a backup of your current jar file if you have any mods installed that you don't wan't to lose. Choose a version from the list, click on "Change" then let Minecraft Version Changer do the work for you.
What's new in this version:
Version 1.3.2_1 adds Version 12w04a and Server 12w04a.