Dynasty leagues are, without a doubt, the fastest-growing segment in all of fantasy sports. The concept is actually quite simple. Draft your startup team, compete all year and keep your entire team the following season. You add to your team in the offseason through an annual rookie/free agent draft, which occurs immediately following the NFL Draft.
I'm in over 10 dynasty leagues and I have gone through the rankings pretty extensively with a lot of new movers to give you the most up-to-date information possible. Remember, these are based on perceived trade value, therefore the rankings are primarily based on what it would take for me to move the player.