Money Saving Websites for Travel

Airlines

farecast.com - Pinpoints the cheapest dates to travel.
yapta.com - Tracks airline prices and alerts you by e-mail if the fare drops. They even monitor fares for you after you book, and notify you if you are eligible for a travel voucher.

Car Rentals

breezenet.com - Discount car rentals

Eating Out

opentable.com - Allows you to view the menus from thousands of restaurants online.
mykidseatfree.com - Show restaurants that have free or discounted meals for children.
kidsmealdeals.com - Show restaurants that have free or discounted meals for kids.
freebirthdaytreats.com - Show restaurants that give free food for birthdays.

Know of any more? Let me know, and I'll add it to the list!