I use Revolution on Tito & Sophie. It's topical - you squeeze a tiny tube of liquid onto the back of their necks once a month. Since it's on the backs of their necks, and such a small amount, they can't lick it off. It absorbs very quickly.

Here is a short description of what Revolution kills:
"Revolution is a topical parasiticide that is applied to the skin of cats eight weeks of age and older to kill adult fleas and prevent flea eggs from hatching. Also prevents heartworm disease and treats and controls ear mite infestation and intestinal worms, roundworm and hookworm."

It's not cheap (about $11 for one monthly dose) but it's worth it. At least that's what I tell myself