I am currently an undergraduate junior. I have taken most of the standard undergraduate math courses and a few introductory graduate courses (measure theory, algebraic topology, complex analysis, analytic number theory). I am very interested in grad school but I have not completed any research and would like to get a start on some during my senior year. My interests are nearest to number theory and combinatorics, though my heart is far from set on either of those fields and I am completely open to looking into research in other areas. I have so far taken three introductory courses in number theory: elementary number theory, algebraic number theory, and analytic number theory. I have only taken a first course in combinatorics, so research in combinatorics may not be viable.
During spring break, I hope to get a glimpse of a variety of research level topics so I can see what interests me the most and get an idea of what I could work on next year, and potentially start on this summer. Are there any books or other resources that would be particularly well suited for someone in my situation?