I'm surprised no one has mentioned Comfortis (Spinosad). It's relatively new but it's similar to Capstar except it has memory. It's a chewable tablet, Starts killing within 30 minutes, kills all fleas within hours, and lasts a full month. The main ingredient is environmentally friendly (even organic farmers can use it on their crops.)
The vet I work for swears by Frontline (Fipronil), but i don't like it. Too many complaints about resistance.
I've always used K9 Advantix, which gets rid of Fleas, ticks, mosquitoes and now it's labeled for Biting Flies.
As ruffmutt said above Advantage does only Fleas, but Advantage MULTI gives you flea pvt, heartworm pvt, and intestinal parasite pvt in one. Also talk of it helping with demodectic mange.
ProMeris is a good product too, but a lot of people don't like the eucalyptus smell or the lethargy side effect. It goes away within a couple hours but it still tends to put people off. But it's great for fleas, ticks, and demodectic mange.
Revolution is a good HW prevention but I don't think it's very effective on fleas.
I don't like Program or Sentinel, or any of the growth inhibitors because they don't KILL the fleas, they just keep them from reproducing.
PREVENTIC collars are great for ticks. Though flea collars usually don't do any good.
And as other people have said above, only 5% of fleas are on your pet, the other 95% are in the environment so you have to treat your house as well as your pet if you have an infestation.