It's been about a year since I graduated with my mathematics degree and due to work, I've pretty much stopped learning mathematics entirely. I'm sure I have not learned a single new theorem since I graduated.

However, I want to apply for scholarships for 1-2 year master programs next year so that eventually I can get back into it and not think about the real world for a couple of years. What are the best books to prepare me for this? I would really hate having to catch-up once I'm already there when really have 1-2 years for preparation right now. Any recommendations would be appreciated.