This a good article, Tinkering With a Longer Season, from my new favorite blog, besides this one, The Fifth Down.
Tinkering With a Longer N.F.L. Season - NYTimes.com
A couple of options:
17 Game season
18 Game season w/ players playing a maximum of 16 games
17 games w/ a nuetral site game
The best thing I took from the article: Fans don't want 18 games, they just don't want to pay full price for a preseason game.