More and more, I use ITN, owned by American Express. It shows availability by fare basis, which is important for determining whether the possibility of an upgrade may be available for a particular itinerary. Their hotel engine is a lot better than either Expedia or Travelocity, as it shows which hotels are available for particular dates. With Travelocity and Expedia, you bring up a set of hotels for a city and then have to check each individual hotel for the dates you want. Expedia's "check availability" dialog is so poorly designed it can't even remember the date you typed in from hotel to hotel, so if you want to check 4 or 5 hotels' availability for the same set of dates, you have to keep typing in the date. (You didn't have to do that with the previous version of Expedia, by the way.)

I still use Expedia and Travelocity, and occasionally the airlines' own web sites, to check flight availability more out of habit than anything else.

Tute: Expedia is 86% owned by Microsoft. Anti-trust agreement? Huh?