/sci/ - Science & Math

I posted in the other thread but this seems to be the right one.

Looking for a recc for a subject to learn. It will be through self-study, so any texts would also be welcome.

I know the basics of algebra, analysis & topology, with a little more depth in commutative algebra and algebraic number theory.
(i.e. taken pretty much all the typical "undergrad" courses)

What should I check out next?
I'm taking an alg. geometry class next semester so I figure I may as well just wait to learn that.