You can write a thesis that focuses on any of the primary literary elements. For example, plot structure, character, theme or style would all make a good starting point for a thesis. Usually, a thesis like this will have to compare different examples or be a broad examination in order to provide enough subject material. For example, "An Examination of the Classically Defined Tragic Hero in Modern American Literature" would be a way to examine character in a way that would provide plenty of material for a complete thesis.
Many college-level classes analyze literature from the standpoint of geography or period. For instance, "Late 19th Century American Literature," or a class very much like it, would be a class found at colleges across the country. So, choose a thesis that examines a specific period and place that is associated with famous literature. "Playwriting in London in the Early 20th Century" would be one example. Also, look at the place and time that are used in a book rather than those that the authors lived in. For example, "The Use of Dialect in Novels Set in the American South" could prove a worthy project.
People write as a response, commentary or reaction to various political and social events. As a result, there is a healthy body of literature with this point of view. Look at the connection between the political, cultural or social movements of a given time period and the related literature. "The Response to McCarthyism Through American Literature" would provide fodder such as "The Manchurian Candidate" and "The Crucible" for a student to look at.
Authors who were prolific provide the thesis-writing student with numerous opportunities to create topics. Combined with elements from the previous topics, a look at a particular author is an effective starting point for a thesis. "Insights into the Historical Figure of Shakespeare Through his Writings" would include elements that would have to look at life in the late 16th and early 17th centuries in London in order to draw sufficient conclusions. By the same token, "The Politics of Twain" considers the political climate when Mark Twain wrote and his personal beliefs that shine through in his work.