Craig M. Booth has done some very nice visualizations on this subject [1]. I found this chart comparing height/weight of 2013 rosters by position [2] particularly interesting and this set [3] covers a question that anyone who has read Outliers has probably wondered about.
1: http://www.craigmbooth.com/category/nfl/
2: http://www.craigmbooth.com/height-and-weight-of-every-active...
3: http://www.sportsballweekly.com/the-relative-age-effect-in-p...