Hey bachr1989- from what I've been told, the writing sample is one of the most important parts of the application. Essentially, the admissions committees want to know that you're capable of intelligent arguments based on original research (which, ideally, would include both extensive primary and secondary materials), since a big part of grad school is completing a dissertation (aka a big walloping research/writing project). If you have a senior thesis, that might be the paper to pick, but it sounds like you're stuck in a situation where you don't have one. If nothing you've written immediately springs out at you as "the piece of writing that will make you shine for the adcom", you can write something new. It sounds like you might be on the path to doing that. If you know that your research paper that you're writing right now absolutely will be done by mid-November, there's no reason why you can't complete the rest of your apps in the meantime and then submit them when you've got there paper done. If you're really worried about it, maybe think about editing through another paper you've written and are fond of.
Some things to think about:
-Primary and secondary research: show that you know how to work with primary sources and that you can familiarize yourself with the academic discourse on a specific topic
-Target length abt 20-25 pages: Any longer and you end up running into page length limits (or having to excerpt), any shorter and you don't show off yourself to the best of your ability.
Don't worry if your writing sample isn't necessarily on what you want to study in grad school . For example, you want to study the cultural impact of Otto van Bismarck, but your paper is on American political discourse in the 1890s- it should be okay (caveat: unless the program specifically requests a writing sample relevant to your proposed research, in which case, do what the nice people have asked).
Definitely ask a professor (or two, or three) to read through your writing sample for you.