Fantasy today is almost overwhelmingly tinted by a few literary influences which, while not surprising, are hardly the entire gamut of available literary influences that it could have. To a certain extent, this is becoming less true in fantasy fiction, as slightly more outre settings have made some headway in recent years in the market. To a certain extent this is also true in the do-it-yourself RPG market, where "amateur" RPG designers release work via PDF. Here I'm thinking of stuff like Weird Adventures, or Tales of the Grotesque and Dungeonesque as two works that build off of something other than standard fantasy conventions. And while nice examples, they are also not unique. In mainstream gaming material, however, very conventional fantasy seems to be ubiquitous, and mainstream fantasy literature still puts out much more conventional fantasy than anything else. And probably always will, until there's a major sea change in the genre.
The modern fantasy genre really starts with William Morris and George MacDonald, and as such, is heavily rooted in a late Northern and Western European Medievalist perspective, combined with some of the fairytales that would have been current during that same time to give it some supernatural spice, and the creation of a secondary world. This high medieval coupled with fairytales approach is still one of the major influences in fantasy today.
Robert E. Howard and the rest of the sword & sorcery crowd, on the other hand, were big fans of an Orientalist approach to fantasy. Clark Ashton Smith was a noted fan of the earlier novel Vathek, and H. P. Lovecraft went so far as to write more than one story that is sometimes considered almost a pastiche of Vathek. (The DreamQuest of Unknown Kadath). In both cases, high medieval of northern and western Europe, or Orientalist approach, the elements of the past that were borrowed were, of course, highly romanticised, which also remains a common theme in fantasy today.
Tolkien, Lewis and his crowd were fans of "the Northern Thing"--unsurprising, given Tolkien's occupation. Tolkien's romanticized Dark Age fantasy, complete with fairly transparent analogs of Vikings, Anglo-Saxons, and lots of northern saga and mythological additions--famously elves and dwarves, of course have had an indelible mark on the genre, to the point where some folks think of elves and dwarves as almost synonomous with fantasy.
In some since, the romanticization has faded--the prevalence of much darker themes, anti-heroes and whatnot being a notable movement in fantasy today. To some extent. But otherwise, the notion that fantasy is kind of a mélange of viking sagas, high medieval romances, picaresque Orientalism and modernized mythology via a Tolkienian perspective is not. Naturally, this is a fairly short list of major influences. Why so short? The only real sizeable exception to this is the low fantasy subgenre, which is flooding bookstores today with sometimes semi-romance supernatural modern era books, embodied by series like Anita Blake, Twilight, Dresden Files and more.
What's somewhat surprising to me is that the very rich and varied mode of adventure tales hasn't been better tapped to provide fantasy with a significantly different feel that this kind of Medievalist fairytale influenced fantasy. Why isn't there really much in the way of Western influenced fantasy with cowboys and indians? Swashbuckling fantasies with pirates or musketeers? Noir fantasy with hardboiled fantastic urban environments (actually, this is starting to gain some traction in just the last few years)? Spy fantasy, or cops and robbers fantasy? This rich potential market is served, if at all, by very niche, DIY type products only.
Anyway, I'm not putting out a call for action, or anything, but just curious and thoughtful a little bit at this vast untapped sea of influences that could greatly enrich the fantasy genre--but which remains only lightly tapped today, for whatever reason.