Graffiti.net is also really good and simple to use. I didn't get spam until I started applying for scholarships off fastweb.com. I think half those places took my info for that purpose.
Other than that, graffiti has excellent spam control and never gives me any trouble. I don't know if this is the best you can get in free space, but I have 250 MB. I noticed that if you "delete" something, it goes to the trash and stays there forever. It never goes away and it doesn't count toward your available storage space. Plus, the name sounds cool.
