First of all, I want to say that it's important to study for both the general AND subjects tests. I know of several people who focused their studies on the subject test and neglected studying for the general test, with unfortuantely poor results.
Don't assume that because a graduate program requires the subject test that they won't even care about the general test. Yes the GRE subject test is important, and it is supposed to gauge your competence on physics, but the GRE general test is important as a measure of your general math and english abilities. Why do you need to know your algebra, arithmetic, and geometry? Well, that's obvious. But why do you need to know your english? Because as a graduate student, you need to WRITE well, because that's what graduate research entails -- conducting experiments followed by documentation and, eventually, publication!
Of course the grand-daddy link of them all:
Here are some useful links for the subject test:
http://www.wpi.edu/Academics/Depts/Phys ... e/gre.html
And here are some useful links for the general test: