Dissertation

So - I made a start. I have 'mind-mapped' my main ideas and dug up an initial dozen or so papers to start reading through. Seems like there is one main author that has worked in the field I am investigating as his name keeps popping up everywhere - K will be proud to hear he is Scandinavian. The only problem I have now is that my (I thought) quite focused plan keeps spawning new areas of interest as I read through various papers. At some point I will have to get strict!

Anyone know any good/free software to track papers, their authors and contents to make my bibliography grow over the duration rather than being a mess at the end of it all?