Oh, if you really want to study lots ...
I have two older brothers, and I swear we own every prep book on the face of this earth. For Math IIC:
REA SAT MATH IIC : Good for practice problems, actually, but no prep for specific sections. PR
SAT II Math WorkOut: Separate from their SAT II math book, this has less conceptual review and more practice. Extremely easy but quick and good review.
Barron's: As always, overpreps.
Kaplan: Nice - not very good at teaching the material but good practice.
There are others, but none seem to stick out in my mind.