One of my favorite settings to come from any recent television show or book is that of Avatar: The Last Airbender (and its recently-started sequel, The Legend of Korra). Historically, D&D hasn't handled the mastery of a single element very well - until now. These houserules modify the Elementalist class to better reflect the setting of these shows.
The ability to manipulate a single element has been woefully lacking in most versions of D&D (fire notwithstanding), so imagine my excitement at hearing of the Elementalist Sorcerer in Heroes of the Elemental Chaos. Upon reading the class, however, I was disappointed – I was hoping to be able to make a character straight from Avatar: The Last Airbender, and while the Elementalist is the closest I've ever seen in any official D&D book, I was still left disappointed.
These houserules address that deficiency in a number of ways;
• by shuffling around the favored damage type of each element – lightning being associated with air and earth with acid are system artifacts I didn't want.
• by replacing the generic Elemental Soul damage resistance features with more unique, element-specific features.
• by restricting at-will choice and reflavoring some existing at-wills to further differentiate the elements (and to prevent intermixing).
• by removing the ability for a fire elementalist to teleport – perfectly logical in D&D, but out of place when trying to evoke the feel of Avatar: The Last Airbender.
• by adding a basic elemental-themed cantrip to each specialty to further evoke the show's feel.
• and finally, by offering a hybrid version of the class to allow for flavorful combinations such as Monk/Elementalist (for most of the combat-focused characters in the series) or Cleric/Elementalist (for a Water Tribe healer).