League of Legends, the spiritual successor to the popular Warcraft III mod Defense of the Ancients, is going free to play, with an item shop. When the game comes out this September, you will be able to acquire the game free of charge, though there will also be a Collector's Edition retail product available at BestBuy and GameStop that will contain extra goodies.

The Collector's Edition will include numerous extra Champions, Runes (champion augmentations), several unique Champion skins, and Riot Points.
League of Legends will feature two types of game currency, the first is the aforementioned Riot Points, which are acquired through play, but can also be purchased with real money. The second is Influence Points, which are acquired only through playing actual games. Both forms of currency will be usable on the League of Legends store, but only Influence points can be spent to acquire both visual and gameplay upgrades. This will keep the playing field level as players who purchase Riot Points will only be able to spend them on novelty customizations such as visual effects for their Summoners.
The developers will also be holding an IRC chat this Friday, July 17th 2009 from 2-4PM PDT to discuss the Summoner system and take questions from the community.
Details on the Summoner system can be found here.
For more information on the Summoner reveal chat, go here.