Flea bombs are a way to deal with insect infestations that basically spread a fog of insecticide through your house. They can be one of the more effective ways to kill fleas, because they'll get all the eggs as well, but they are also one of the more annoying because you can't be in the house while they are going off.
If you're going to use one, follow the instructions closely on staying out of the house. Keep your pets out of the house as well. You should also give your pets a flea dip or bath just before you set it off, because if you don't your pet is just going to bring the fleas right back in. Also be aware that if you've got a dog or an outdoor cat, you need to do something about your yard as well - flea control nematodes and diatomaceous earth work well for killing the fleas in your yard. If you don't get the fleas in your yard, again you'll have a new source for them to come back into the house.
Usually a bomb will take some time - 8 hours or so is standard I believe.
Here are a couple you can take a look at:
Zodiac Fleatrol Fogger / Flea Bomb
This one is available here online and it costs about $13.00. It will kill all kinds of other bugs like ****roaches, spiders, and ants as well. The other good thing is that it's got insect growth regulator, which is a chemical that stops fleas from growing to adulthood. That will basically cut off the life cycle of the fleas and stop further infestation.