If you're the kind of student that has done the research early and you know what you're interested in studying, then you might be a good candidate for an early decision or early action program. It varies depending on the institution, but most programs allow applications as early as November and notifications are sent in December or January. The rules for each program will vary from place to place, so check with your guidance counselor or the university you're interested in for the specifics. The one thing they have in common in most cases is this: Early decision programs are binding; early action plans are not.
Early decision programs allow a university to extend early admissions and financial aid packages to students committed to attending the school. You can only apply to one school as an early decider, so it should be your first choice school. You can apply to other schools as a regular applicant. But those applications must be rescinded if your early decision school admits you. Most colleges require some kind of nonrefundable deposit to ensure this.
Early action plans are similar, but they do not require a binding commitment from the student. Upon acceptance you can choose to make the commitment right away, or you can wait until the spring. You can also apply to other schools as an early action applicant. Some schools offer a variant of the early action plan called single-choice early action. This is when you agree to not apply to other schools early, while maintaining the right to apply during the standard admissions time frame. Under the single-choice plan you can still inform the early action school of your decision in the spring.
Critics point out that it may hurt students who depend on financial aid by committing too early before all of their aid options are explored. Harvard University discontinued its early application programs in 2006, claiming that it tended to "advantage the advantaged" [source: Starkey]. This had led other universities to examine their own programs. Right now there are still more than 400 schools that offer one or both of these plans, so check with the schools you're interested in to find out if they are a participating university.