http://www.footballgeography.com/nfl...neutral-sites/ (you can click on a column heading to sort)
The above link is an interesting history lesson. NFL teams used to barnstorm. I read that sometimes players used to get up to 25K to play in these neutral sites.
If you think about the sports landscape back in the 60's and early 70's, baseball was probably more of the leading sport, so you can see a publicity tour of exhibition games to grow the popularity of the sport. If you go to the link above and see some of the stops that teams made to play games, just imagine today's players doing this. Some of those places wouldn't be terribly easy to get to.
Here's some AFL vs. NFL exhibition history: http://www.remembertheafl.com/AFLNFLexhibitions.htm