I’ve found it varies, like no one site has the cheapest consistently, and I try several sites to compare. Some sites will price-check multiple sites for you, I guess like Kayak (never used it, but I will have to bookmark it), such as FareCompare.com.
@MissAnthrope I’ve always wanted to go to B.C. (British Columbia), and Cali is close.. We could always meet there, lady. A lezzie vacation in Vancouver, perhaps. =) My girl and I would totally be down.
Kayak is good but I find their UI quite complex to use. I generally use orbitz.com and a mobile app called on the fly from ITA – this app has a cool design and simple grid of options to start with and helps narrow options fairly quickly.