Is there a recommendation for one of the free online file storage services (I don't need to save that much) that I could use with my Mac BUT also:

a) Has the ability to specify a directory on my Mac to synchronize - after which every so often the solution would have a client side small application that monitors the directory and if there is a new file synch this back to the online back up service

b) Ideally also has a Windows client side download too - i.e. can then access files from both Windows and Mac computers