The best travel site for making itineraries is clearly Tripit. While I am not big on social networking sites to begin with, this is clearly better than most as it provides a service which to my knowledge nobody else is providing. You merely forward the confirmation emails to it from various travel sites and it puts them together into an elaborate inventory.
For example, I built an itinerary with hotels from Expedia, Orbitz, Marriott, and United Airlines and it put them all together into a beautiful itinerary with maps and directions. it also integrates with other sites for content. While still in beta, it's a winner. I expect they will get bought out very soon by someone else, but this site does get the Kosher Wisdom Seal of Approval.