Below is a list of free PDF printers, as well as links to their respective websites:
PDFCreator - This is my primary recommendation. You will, however, need to be careful during the installation to uncheck any unnecessary items such as toolbars or additional pieces of software. If you are careful during installation this is a very good and stable print driver.
BullZip PDF Printer - This is another very stable driver. I have only used it a few times, but had no complaints. As with PDFCreator, you will need to be careful during installation to insure that you don't install any unwanted additions.