In my previous post, I talked about how to split PDF files on Mac OS X, Linux and Unix. In that article, I mentioned a simple app that allows you to merge several PDF files. The app is dead simple, and you can create it for yourself if you’d like (here’s the workflow in Automator). All it asks you for is the input files (the files you want to merge), and it will take care of the rest. When done, Preview will pop up with the merged file. You will then have to save the file.
You can download the application from here. It works on Snow Leopard, and I’m not sure if it will work on earlier versions of Mac OS X.