I've used Serfas Seca tires (puncture-resistant model), too, and they seem to be very flat resistant. 700 x 28 tires; I don't like using anything narrower than a 28 for comfort purposes.
I also use Vittoria Randonnuers (700 x 32 or 35) on a light touring bicycle, and haven't had any excessive punctures with them, and that includes riding on some pretty trashy roads.

Note about Vittoria tires: I've found they are quite 'rim-sensitive'; they're easy to get on/off of some rims, but almost impossible to get on/off on other brands of rims. This has occured more frequently with their narrower tires (23-25s). If you do by a Vittoria brand tire check that it will work on your rim before going out on the road with them - its a PITA to deal with a tightly fitting tire while sitting on the curb with traffic streaming by.