I've gotten at least 25 magazine subs free from signups on Freebizmags or other places. Some of these are rather limited in scope [Potentials, eWeek, Communications News], and others are more open [gaming mags, The Week, Cruise Travel, Budget Living, etc].
I'm currently getting Maxim until May of 2010 since whenever I see it offered, I sign up, and they keep adding it. I haven't gotten any of the DVD's or game demos, but I don't complain too much, since hey, they're all free anyway. The way I look at it, if I get it, cool, if not, oh well, I wasted four minutes filling in a form.
If you already had a sub to a mag that you signed up for free, check your expiry date on your address label--they usually just add a year or two onto it, without really doing anything noticable.