I just looked at this thread for the first time today. I checked out the offer for Horticulture magazine in post #301 and found that it still works. Thanks lin821!
At the end of the sign-up process I was offered four more free subscriptions for six months. There was a long list of magazines to choose from. The catch was that after the six months there was automatic renewal, and a credit card was required. I passed because I know I would forget to cancel before my credit card got charged for the renewal, but it might be good for someone who is better at keeping track of such things than I am.