College Board

http://sat.collegeboard.org/register

The College Board; online registration for SAT Reasoning and Subject Test.

Practice for the SAT

http://sat.collegeboard.org/practice/

Practice test, daily questions and more for the SAT. 

ACT

http://www.actstudent.org/

Online registration for the ACT test.

Practice for the ACT

http://www.actstudent.org/testprep/index.html

Practice test, daily questions and more for the ACT.