The Sporting News offers traditional leagues, and several salary cap based leagues, with the latter featuring cash prizes for the participants (even in those that are free to enter). Access to most of the information on players at this page will cost you, but it is very thorough.

NFL Fantasy Football benefits from having the official league seal stamped on it, but is not terribly deep in options. It offers only two types of leagues: one traditional and one salary cap. There are prizes for weekly and overall winners.

ESPN Fantasy Football is deep in information, but also expensive. If you are willing to pay for your fantasy league, however, it may be worth it. Many helpful figures, such as injury reports, likelihood of a player having a good game against a particular opposing team, and player comparisons, are free and can be used by owners visiting from other fantasy football providers.

Fanball offers several innovative free games, such as "Bid2Play," which is a salary cap league where the drafts are handled like auctions. Instead of charging for the leagues like ESPN does, Fanball charges for the information they provide to help owners make better decisions regarding what players to play and/or acquire.

Yahoo Fantasy Football is very similar to Fanball, providing free leagues and pricey features. This site is arguably the easiest to navigate, but probably because it is less in-depth.