I thought I had found all the travel search engines..then someone turned me on to www.qixo.com
It's really great...enter your city pair and dates, (plus number of stops or non stop and time of travel) and it searches all the major airlines, PLUS all the discount airlines, PLUS orbitz. Truly comprehensive...I did a couple of test runs on routes I fly often and it put together some great stuff I wouldn't have thought of.
It can also do a search over a period of time for you at a price you want to pay...a truly great alternative to priceline and hotwire which are such "blind" choices...
Check them out....
Queen of Bermuda, New Years '89
Explorer of the Seas, 9/7/02
Queen Mary 2, 1/31/04