Not necessary "the" best site for finding last-minute cruises - but, we use this site to track historical changes in cruise pricing for all specific cabin categories, etc. No advertising or registration required - once you come up with a short list, the hard work begin but these days, there aren't much price differences on what a good online TA will be charging - more of a question of whether they can still get you some extra/bonus OBC & perks.
www.cruisefish.net
And, if you own stocks in some of these lines - the shareholder perks or benefits can come in handy as for say, CCL - it's another extra $100 OBC to spend on the ship, it usually is taken care of in a day or two, well before that last minute sailing while you are still busy packing & finalizing plans.