TINYPDF is one of the best PDF writers available on the net. It is standalone, very easy to install and use and has a very small footprint (memory usage).
I used CutePDF, which is another free PDF generator, until I stumbled across TinyPDF.
Unlike TinyPDF, CutePDF requires you to install a separate GhostScript application thus my preference for TinyPDF as there is one less application hogging my memory especially since these are idling in the background all the time.
Best of all, TinyPDF is totally free for personal and commercial use.