I've used Frontline on my pup, and it seems to work pretty well. However she does spend a decent amount of time outside (walks, dog park, etc) so by the end of the one month cycle they seem to come back. I also give her flea baths to try and help with it. Also, I've started looking into something called Sentinel. It's a combined flea and worm medicine tablet. I'm not sure if they make it for cats though.