I am excited to see what it might be--are you? (Suggestions?)
Start planing (and applying) early--talk to several of your professors about advice. Definitely consider differentiating yourself by attending one (or more) REUs (Research Experiences for Undergraduates) or doing undergraduate research with a faculty member. Look at the AMS for Students site for more specific information.
A few of the many websites a mathematics student should know and use. You should belong to the first of these--majors should ask the chair about a free membership. Google Scholar and MathSciNet work better than simple internet searches for finding articles (and both can display appropriate references!)