I use Frontline, but only a few times a year, as needed. I used to get it from Pet Shed, but found that Pet Care Choice was cheaper and they are just as fast with free shipping for a year on orders over a certain amount (I think it was $100).
I've noticed a huge difference since my previous kitty, Jasper, was still alive. He was an outdoor cat and though he never had fleas, he did carry them in to the house and they just went after the labs. Part of the reason why Phoebe is a strictly indoor cat.