early...what? types of admission submissions for college

Early Decision - Early Decision means that if you are accepted to this school, you must go unless you cannot pay for it financially. DO realize that if you apply early decision, you ARE still allowed to apply to other schools with Early Action, but NOT Single Choice Early Action. (This is not suggested, but it is allowable.) ALSO realize that if you are a financial aid candidate, you are allowed to apply to other schools regular decision because of financial concerns. Make sure if you apply early decision, you really, truly want to go to that school. It might seem like a good idea to "play the college admissions game" and be admitted to a top-tier school/ivy simply because the early decision rates are higher than the regular acceptance rates, but you are bound to go there and there are no "take-backs". Schools with Early Decision include Cornell, University of Pennsylvania, Amherst, Swarthmore, and Washington University in St. Louis.

Early Action - Early Action means that you are simply submitting your application early (sometime around November 1st), and that you will receive your decision earlier as well (sometime in mid-December). I'd say this is the one that I see absolutely no harm in doing unless you'd like to significantly boost your application through new SAT scores, etc. Some schools that offer this include University of Chicago, University of Michigan, MIT, and Harvard (which has JUST reinstated it for Class of 2012 high school seniors!).

Single Choice Early Action or Restricted Early Action - SCEA means you can only apply to one school early, although you can still apply using priority applications (especially for state schools.). On the bright side, if you are accepted, you are not binded to go and and take it easy, apply for more reaches if you wish.  In my opinion, SCEA is unhelpful unless there is no other school you see yourself in (and this choice is the only thing offered by the college) or if you are legacy. The restriction of applying to one school early action means that you miss the early application of lots of other schools including those listed above. Furthermore, especially with the top-tiered schools, you'll see the admission rate staying pretty constant with the regular decision acceptance rate. From my experience, legacies have had an advantage in this process. Some schools that offer SCEA include Stanford, Yale, and Princeton (just reinstated for Class of 2012 seniors).
*Suggestion: If you take the SCEA route, I recommend writing your other supplemental essays for reach schools you may apply for if you are accepted during the wait time. Many students, after being accepted into a top-tier college, lose the motivation to write more essays and then just don't end up submitting an application. I personally think having a choice is better than having no choice at all.

Priority Application - I have found no disadvantage in applying priority. Usually, you reap benefits such as scholarship consideration, obtaining an earlier admission decision, etc. Do be careful and make sure the priority application is non-binding though! Also, you are allowed to apply priority even if you have applied Early Decision OR Single-Choice Early Action! Schools include St. John's, Tulane, University of Florida, University of Maryland, etc.

Rolling Admissions - Admissions come out in waves, usually with a deadline given as the last day. This is nice because you receive a decision earlier than you anticipate and being accepted into a college is always a huge relief because at least you'll know "Alright. I can relax. I'm going to college."