WikipediaYou already know it and love it. Don't get it twisted: this still isn't an appropriate source for your final product. But for getting ideas to bounce around? Go for it!
Wikipedia lacks authority because anybody can edit it. Further, and even more importantly, it's an encyclopedia: it gives you a lot of information without analysis. For college-level research, this isn't the kind of source you should be drawing on. Encyclopedia Britannica and Webster's wouldn't make good sources, either.