i've used expedia and priceline.com. i love priceline cause you get your tickets cheaper.
I forgot, i've used cheaptickets.com also.
I just got tickets to Costa rica using expedia--great prices, too. I'll tell you how good things go. In the past I've used priceline, cheaptickets, and several others to get my tickets, but never with the hotel included. All have worked out relatively well. One time, though, I got sent to Texas for my stop over to Vancouver....that's a little ridiculous.