MICUSP, the Michigan Corpus of Upper-level Student Papers, is composed of papers with a grade of A from the University of Michigan written for upper undergraduate and early graduate courses. This searchable database makes it possible to see disciplinary differences in academic writing, to observe the various ways that a particular word or phrase is used, and to pull out features of particular papers, such as those with citations or strong argumentation.
The search interface in MICUSP is largely visual, making it pretty easy to navigate through the various options for narrowing and refining searches.