The best and most authoritative source of information is the MSAR. You might as well spend the $25 now, because you're going to be referring to it often in the coming months.
As a general rule, though, the vast majority of med schools have rolling admissions. The non-rolling schools tend to be the most elite institutions, like Harvard, Yale, Cornell, etc. And even with those schools, INTERVIEWS are granted on a rolling basis, so the earlier you apply, the better.