fftoday.com (free) and footballguys.com (paid) are both very good and have good forums. Fftoday posts weekly rankings of players.
Unless you are really into the details I would skip buying any kind of magazine, I am actually surprised they are still in business. Those things are done way early after the draft and so much changes by the time real drafts come around the ranking are not worth anything. The information about new offense and def coords or new head coaches is valuable but too much has changed for the ranking to be relevant.
rotoworld is also great on updates, but you have to be careful about reading into their analysis their waver very quickly.
Also I posted this on the fantasy forum, but I put together team by team projections for the season its excel based, and can be customized to your league scoring.
I also use it as a main guide for when the NFL player futures come out, or for offensive rookie of the year.
http://ffslickpicks.com/page/2014-FF-Stats.aspx