With more than 900 inbound and outbound flights per day and nonstop service from more than 130 U.S. and international cities, Las Vegas is efficient and cost effect.
For domestic flights, Southwest Airlines usually has the most competitive air fare. You also get to check on 2 bags, and have 1 carry-on and 1 personal item. Subscribe to Click N' Save and monitor the low fare calendar for the best prices.
If your airport is not serviced by Southwest or you are international, check out Kayak. Kayak searches across all airlines.