To begin with, Tolkien and Lewis, writers of The Hobbit and The Chronicles of Narnia respectively, did influence some well-known and not-so-well-known stories, almost all of which are of the fantasy genre. One example of Tolkien's influence is Dennis L. McKiernan's Iron Tower trilogy which "was intended to be a direct sequel to The Lord of the Rings but had to be altered" . The Harry Potter series by J. K. Rowling "mirrors some themes from ideas from The Lord of the Rings" . A couple of examples of Lewis's influence include A Series of Unfortunate Events (Daniel Handler) and even the Harry Potter series. In addition to works of prose, there were also the film adaptations of The Lord of the Rings and The Chronicles of Narnia's The Lion, the Witch and the Wardrobe, Prince Caspian, and The Last Voyage of the Dawn Treader.
Video games based on The Lord of the Rings and The Lion, the Witch and the Wardrobe have also been made. While the video game based on The Lion, the Witch and the Wardrobe has only been made based on the movie, The Lord of the Rings has had video games based not only on the film adaptations, but also the novels--and even games just based in the world of Middle-Earth. These games weren't the only ones based on The Lord of the Rings. It had a much greater influence on games in today’s culture. Because of its influence on fantasy, the late Gary Gygax was driven to create one of the most prominent role-playing games of the '90s: Dungeons & Dragons. This game was based on Tolkien's concepts of elves, dwarves, humans, and even hobbits (even though Gygax called them Halflings, they have very similar characteristics to those of the hobbit race). Dungeons & Dragons is still in production today, on their 4th edition of the game (which many avid Dungeons & Dragons players have come to shun). Dungeons & Dragons, in turn, had a large influence on the most popular MMORPG (Massive Multiplayer Online Role-Playing Game) of today, World of Warcraft. The great Dungeon Master, Gary Gygax, passed away on March 4, 2008 at the age of 69. On March 25, 2008, Blizzard Entertainment, the makers of World of Warcraft, released patch 2.4.0 of the game, which was dedicated in memoriam to Gygax with this paragraph from the patch notes:
Blizzard Entertainment would like to dedicate the patch in memory of Gary Gygax. His work on D&D was an inspiration to us in many ways and helped spark our passion for creating games of our own. As avid D&D players and fellow game developers, we were all saddened by the news of his passing; we feel we've lost a true adventuring companion. Thanks for everything and farewell, Gary. You will be missed. 
So, if it weren't for Tolkien's influence on Gary Gygax, Dungeons & Dragons would likely not have been made, or at least been very different, and if Dungeons & Dragons hadn't been made, then World of Warcraft could very well have been excluded from the history of games as well. It should also be noted that, while Dungeons & Dragons has been and still is a game with a large fan base, World of Warcraft, as of October 2010, has 12 million subscribers.
Several music bands have been influenced by Tolkien, ranging from one or two songs to the whole band's theme. Some examples of this include such songs as "Elvenpath" (by power metal band Nightwish) and a few songs by the rock band Led Zeppelin. Examples of a greater influence by Tolkien in music include: "Gorgoroth take their name from an area of Mordor, Burzum take their name from the Black Speech of Mordor, and Amon Amarth take their name after an alternative name for Mount Doom" .
To summarize what I've explained here, if it weren't for Lewis and Tolkien's stories, Harry Potter and other stories who were influenced by Lewis and Tolkien would likely be quite different, if they even still existed; a handful of video games wouldn’t exist; Dungeons & Dragons, if it actually existed, would likely be radically different; World of Warcraft probably wouldn't exist, at least not how it is today. Lewis and Tolkien were very influential writers on not only the works of fantasy literature today but games that have over 10 million people playing.
 Works Inspired by J. R. R. Tolkien. Wikipedia. 10-15-2010. en.wikipedia.org/wiki/Works_inspired_by_J._R._R._Tolkien#Literature
 World of Warcraft Patch Notes 2.4.3. Blizzard Entertainment, 7-15-2008. 10-15-2010. www.worldofwarcraft.com/patchnotes/patch2p43.html