The new Mithril edition is exclusive to GameStop stores, and while it may not be as valuable as Frodo's life-saving waistcoat, it does provide $50 worth of content for a paltry $29.99. Exclusive bonus items include a Steed of the Horse-lords mount, Path of the Fellowship quests, and 2,000 Turbine points to spend in the game's cash shop. It's worth noting that the Mithril edition is basically a starter kit for the full game, as it does not include the Siege of Mirkwood expansion or the Rise of Isengard expansion. Further details are available at the official LotRO website.
[Source: Turbine press release]