Can anyone recommend good sites to compare internal flights in the USA? Sites I am used to using from the UK are not doing great - they tell me I can't fly direct from Oakland to Orange County when the airport shows me the flights exist!

Thanks!

Bing is probably best for comparison and date finding purposes. I usually use travelocity to purchase but expedia and pricewatch work too. I recommend against orbitz. I've heard a lot of horror stories but I used them anyway on my last trip and they tried to screw me out of $1200. 6 hours of phone calls later they offered me a $25 voucher.... No thanks.