<p>Most want at least 2, but a lot want 3. Some will have specific requirements (a lot want math) but it also depends on the major you're applying for. Do some digging into the schools you might want to apply to and see what they ask for.</p>
<p>If you're strong enough in a foreign language to score 750+, go for it.</p>
<p>Harvard, Yale, Princeton, and Georgetown are now the only colleges that require three; others that require them need only two. Note that vast majority of colleges do not require and do not use SAT II tests for admission. Many that require two subject tests will rely on your highest two for admission but others, if you submit more than the required number, will use them all and thus if you take two and score high and then take a third and score low, you could hurt your chances for admission at some. If you are applying for engineering, math or science check with particular college because those that require SAT II's sometimes require a math and science for those programs but not other programs.</p>