Check to make sure that you don't have water collecting somewhere. Mosquitoes breed in water, which is why they often turn up in the bathroom or kitchen.
If you have pets in the house make sure you're giving them their monthly dose of heartworm prevention. Heartworm is spread by mosquitoes.
I've seen commercials for those little buzzer things you can wear to keep mosquitoes away. Maybe buy a bunch of those and put them around the house? I don't know how expensive they are, so it might not be very cost effective. I hate mosquitoes!