We had the same problem a couple of years ago. It was AWFUL! We used a company called Fleabusters, their product is basically borax that has like a static charge, so it really stays on wherever they apply it. It's non-toxic, more expensive of course, but it was worth it to us. A couple of months after the first application we still saw some fleas (it was a really, really bad infestation) and they came back an did a second application at no charge. After that, they guarantee that you will remain flea-free for one year. It's been 3 years now I think, and there has been no return of fleas, and a friend who used the same company said the same thing.
Also, frequent, thorough vacuuming has been proven to eliminate at least 90-95% of fleas (that's probably where I slacked a little bit... :) ...)
It's also important to see if you can find the source of the fleas. For us, it was the "beauty bark" so popular in flower beds here. I found out from the nursery where I shop that beauty bark evidently harbors fleas and their eggs, and that's where our pets were getting them. We have since gotten rid of the beauty bark, and have not had any more problems (knock on wood) since. Good luck!