PAPERS: BEST .PDF MANAGER BY FAR

I'm always looking for ways to organize my .pdf: I collect them (JSTOR and "print-->save as-->.pdf" mostly).

Papers is that holy grail. It acts like an itunes/iphoto app for documents. 

Best of all, it will allow you to search Google Scholar, JSTOR and other sites to get the meta data for those .pdfs that download with only numeric nomenclature (an annoying feature of JSTOR). 

Caveats: it is mac only and licensed (but fully functional without actually purchasing the license). 

In fact, it's so good, I'm going to purchase a license to kick a few dollars towards their development efforts.