What mathematics can be interesting for these CS areas?
For the field of A.I. and machine learning, I would recommend you to explore and learn more about these topics:


Statistics
Probability
Stochastic processes
Bayesian Data Analysis
Convex Optimization
Graph Theory


With your math background, you could easily pick any good machine learning book and learn the required math that you don't have as you go. Kevin Murphy's new book, Machine Learning: A Probabilistic Perspective, covers most of these topics and it serves as a good introductory textbook to machine learning.

I personally learned a lot from Dephne Koller's book, Probabilistic Graphical Models. It also covers most of the previously mentioned topics, but, as the book's name suggests, it focuses on graphical models.  

Although both of these books have enough math to keep you busy for a while, you might find "The Elements of Statistical Learning", by Hastie et al. more useful if you want to focus more on the mathematical part of the machine learning.