Kayak.com is a “meta-search engine,” a website that allows you to search 4000+ other travel websites, including, hotels and cheap rental cars, for fares and prices all at once.
Kayak.com is not a travel agency, just a web search service. If you select a service, fare or price, Kayak redirects you to the website where you can reserve the flight, hotel room or car rental.
It seems to work great! I find its layout and presentation easy to use, and its results surprisingly accurate and helpful.
If you’re looking for cheap flights I’d suggest that you give it a try, whatever else you may do.
For airfares, it’s particularly good to get a glimpse of what current airfares are between certain cities, and which airlines fly that route.
You can also request periodic email updateson fares.