The University of California system is dropping the requirement that applicants must take two SAT IIs (in addition to the SAT I) for the high school class of 2012. This means you may not have to take any SAT IIs. HOWEVER, they are still recommended for some majors at some of the UC campuses and you may need to take them for non-UC schools which you are applying to as well.
It is fairly crucial to have decided what schools you are going to apply to no later than the summer of your junior year. If you do need to take SAT IIs, you will have three last opportunities to do so in Oct., Nov. and Dec. of your senior year. Keep in mind that you may need to keep at least one of those dates free to take the SAT I a second time as the SAT I and SAT IIs are offered on the same dates. You can not take both on a given day.
The Cal State system and the UC system will continue to require the SAT I.