If you usually deal with a lot of PDF documents in Windows then having the ability to merge PDF files could be a necessity. There are a lot of tools out there that you can use. However, if all you need is to “just” merge PDF documents and only that, then you should try “PDFBinder”.
It is a very simple tool (a front-end that uses a PDF manipulating library called “iText), licensed under the GNU GPL v3 and free to use. Once installed, you can open your preferred PDF files into its window (by using either the “Open” dialog or you can drag-n-drop as well). When done, just hit the “Bind!” button, and you’re done!.
But for the sake of the post, let me write down its features …
*. Add & Remove files from its main window.
*. Change the order of the queue.
Yup, that’s it.
I tested it under Windows 7, and it works (should also work under older version such as Windows XP, Vista too). You can get it from this Google code project page if interested.