Eric,
PDF Creator (
http://sourceforge.net/projects/pdfcreator/). I've used it for a little over a year. It works well (you create pdfs from it by selecting it as your printer in any application and printing to it).
Another one with more features, but a pop-up ad revenue model is PDF 995 (
http://www.pdf995.com/). I use that if I need more advanced features like combingin multiple pdfs into a single file.