Combine PDF’s with Preview by dropping thumbnails onto one another
You can combine PDF files within the Preview app by dropping thumbnails onto one another, Lifehacker explains:
The trick is to drag thumbnails on top of a thumbnail in the document you’re dragging to. This combines the pages. If you want to rearrange the pages, just drag them where you like—they’ll stay within the combined document. Save your document and you’re done.
This is a pretty good PDF management tip and one I’ll be sure to use. This appears to be Snow Leopard only so you’ll need to upgrade if you want this feature.