You say 'as for statistics, I've already taken most of them' but that really means nothing to most of us. Undergrad programs vary A LOT. Do you go to a school that has a separate statistics major? Or is it just a stat concentration within the math major?
It would be better if you just gave us more background on what classes you've taken, what classes are offered, and possibly what classes you think you should take.
Also: what type of grad program do you plan on applying to? Applied or theoretical? Or are you leaning toward biostats? Do you know what research area you're interested in? All of these things could help us tailor our recommendations to you.
Edit: I guess I'll add that a course in real analysis is always helpful.
I took Probability, Statistical Inference, Linear Regression, Computational Stat (using R basically), Categorical Data Analysis, Sampling Theory.
So, I took Linear Algebra, Differential Equation, 2 of the 3 courses on Real Analysis.
I talked to a few people who got in the Masters at Stanford and a few friends applying for Ph.D. Their math background seems to be very strong. My math major friends also have a easier time in stat.
So, I was wondering what math do you suggest me take?
The school is offering: ODE, PDE, Analysis and Optimization, modern algebra, modern analysis. Should I also finish taking the last 3rd Real Analysis class?
If you don't mind me asking an off-topic question, could I ask you where you took the "Computational Statistics" course that you mentioned? Judging by your username I thought of a school but I could not find that particular course at the Statistics Department (or the Math Department) of that school. I am very much interested in taking a similar course (especially one focused on R) and would be really grateful if you could share that information (if you want, you can PM me in case you do not want to post the information in public).
EDIT: Please ignore this post if the school is not located in the Northeast.