What are 3 different online intermediaries that could be used for this incentive trip?You are employed by a large company in its event management...

There are several popular (and free) online intermediary
interactive websites which you could use to accomplish this project.  Most people are
aware of Orbitz, Travelocity, Expedia, Priceline, and Bing.  Each of these companies
searches for the best online deals.  I have personally had the best experience with
all-inclusive trips (as far as price goes) using Orbitz, but on any given day, the
prices will vary with any one of these companies.

As far as
accomplishing your task goes, let me give you a few tips.  I usually start with one
website and type in everything I want (flight, hotel, location, dates, etc.)  I get a
price range by narrowing my selection to my top 2 or 3 resort choices.  Then, instead of
doing a wide "search" on the other websites, you can type in your exact resort name and
dates.  This is the easiest way to compare prices.

Also,
once you've found the very lowest possible price, you can go to the website of the
resort itself and see if there are any "special offers" that beat what you found.  From
experience I know that if you choose to go with Orbitz, and you later find a lower price
or an online deal that Orbitz did not find, they will match it for you and refund the
money even after you've booked.  Perhaps some of the other companies above offer similar
customer service.