There are many programs available for creating installers for your application. Here are a few you might want to look in to.

Windows

• Nullsoft Scriptable Install System (NSIS) - Efficient, scriptable, and free installer builder. I suggest you start with a script generator and then tailor the results. The scripting can get complex, but it is completely flexible. There are plugins for a variety of things, lots of examples and code snippets, and great support in the forums.
• Inno Setup
• Install Creator
• CreateInstall
• Astrum InstallWizard

Mac

• PackageMaker - Included with the Mac developer tools. I suggest keeping it simple and using a DMG for a drag-and-drop install unless you need to do something complex.

Mac/Windows

• Sweat Technologies InstallGadget - Inexpensive, fast, multi-platform. Accepts license and read me files.
• BitRock