1. Check Kayak.
2. If you have a quirky itinerary, you can't beat the secret weapon:
https://matrix.itasoftware.com/ -- it's tricky to use but man, it is the best.
3. Always book on the airline's own site.
4. Be sure to clear your cache/cookies before searching on the airline's sites, because they cookie you and raise prices once they know you're interested in a route; clearing that out resets the prices.
5. For future travel, take a peek at one of the sites I manage, frugaltravelguy.com. You will learn the ways of the force, and become a jedi master.