First off, Al O'Donnell's "Point Spread Playbook" is the best stats book out there with the NC Sportsbook following a close second.
Al's book gives you everything you could want over the last 3 years, trends, stats - everything!, The NC book gives you stats for the last 5, 10 and more years, and systems up the whazoo - but make sure you verify the stats as they're not the most reliable - and many of the systems are out of date and also a bit unreliable if taken only at face value.
For up to date stats, I love the "Mr NFL" program - it gives you all of the important stats in every combination - YTD, last 4, home vs away, etc.
For newsletters, I like Kevin O'Neills weekly the best. NC Has a good weekly with their Power Sweep if you're willing to sort through the grist to get to the grain.
For books on Pro football wagering, I recommend the following:
Kevin O'Neill, Strategies for the smart player, and New strategies for a new era.
JR Miller, Beat the Pro football pointspread
Dan Gordon, Beat the Sportsbooks,
Bob McCune - any of his books (although he blathers on and on before getting to the point)
Jim Feist and Kelso Sturgeon, Football Betting
and
Stanford Wong, Sharp Sports Betting.
Each of these books has something valuable to offer.