pdftk - A handy tool for manipulating PDF
Highly recommended: I use it for concatenating pdf documents, or selecting a subset of pages. I get it via fink, but you can also find it online. Unfortunately,
pdftk doesn't allow you to rotate pages.
Preview.app lets you rotate and save pdfs: ⌘-L, ⌘-R, or use the menu—to rotate a single page, hold the option (alt) key while doing this.