Love cruisecritic!
We just booked a 9 night Thanksgiving cruise out of New Jersey on
Royal Caribbean's Explorer of the Seas. Can't wait!
Wanted to mention that when you are trying to pick a cruise, really check out the reviews for the individual ship you will be sailing on. Even among the lines, ships vary a great deal.
As a general rule...not always though, most of the lines will have their older ships sail the shorter 3/4 night cruises and have their newer ships with more amenities do the 7 night or longer ones.
Once you have narrowed down the cruise you want, I'd also suggest cruisecompete.com. You will be able to get quotes from several agencies competing against each other. They will offer you anything from shipboard credit, to reduced prices on excursions to prepaid gratuities.
Hope this helps!