Like others have said - I would be looking at the environment. Because you are finding dead fleas, the frontline must be working to a certain extent like you said.
I have two dogs I groom every year and they are due back in tomorrow (covered in fleas). The owner uses frontline and even sprayed under the house where she believes they are breeding - but still fleas every where. We are in a rural area, where breeding is accelerated, so it can be a loosing battle.
But a few nature remedies to consider. Add garlic to your dogs food (fleas apparently don't like it) and also if you dog likes swimming, salt water is great for keeping fleas at bay.
I use frontline, but also during the summer months when fleas are really bad, I wash them in a flea wash rather then my regular shampoo and I also wash the kids bedding weekly rather then monthly.
Cheers
Amanda