Coming up with ideas for philosophy papers is just as difficult for those of us who have been doing it academically (and even professionally) for many years.
But if you do a compare and contrast, now you will have to work out getting right not just Kant's position on something, but also another philosopher, who I'm sure is not easy either. Save yourself the time and energy--stick to Kant solely.
Instead of a compare and contrast thesis, how about some contribution in which to you address a particular aspect of Kant's ethics with its relation to another aspect of his thought (e.g., his epistemology, or theory of mind, or theory of language).
Or, you could examine how Kant's ethics contributes to some other area of philosophy in a way that is overlooked or underappreciated. For instance, since you claim to understand Kant pretty well (I doubt this because even scholars have a hard time understanding Kant well), maybe you could argue that Kant's ethical theory contributes to areas of contemporary concern. Perhaps Kant's ethics can have something important to say about philosophical theology or the ethics of belief, for instance. Also, alot of ethical arguemnts have schematic analogs in contemporary philosophy of science debates (e.g., the debate concerning the identification of moral properties is analogous to the identification of unobservables as theorectical entities). Perhaps this could be something (It's a chance to show off your creativity, but be careful, don't go overboard. )
Or, you could just do a simple philosophical analysis paper in which you formulate some argument in Kant's ethics, exegete the argument, place it in context of his overall project, explicate the argument and then crtique it. Formulate the argument according to validity conditions and then argue that its soundness is in question.
In general, philosophical topics most commonly take the following forms:
1 Compare and contrast
2. Argument analysis
3. Clarification of a concept or set of concepts
4. Dissolution of a psuedo-inquiry/debate/problem
5. Postive Argument for a particular veiw
6 Negative arguments for a particular view
As an undergaduate, you will not be expected to contribute novel ideas in current Kantian scholarship. It is usually good enough that you demonstrate your ability to formulate and analize his arguments properly, and that you have an understanding of his veiws and their implications to other areas of Kant's thought, as well as how those veiws might relate to contemporary issues.
For Kant's ethics, a good introduction can be found in the work of Roger Sullivan, which should give you ideas. Also, consider, as indirect material, Dicker's book that is an introduction to Kant's epistemology. The Cambridge Compantion to Kant will have good material as well; and so does the Stanford Encyclopedia of Philosophy (online at http://plato.stanford.edu/contents.html ), and the Cambridge Dictionary of Philosophy (ed) Audi.