I just waged an epic war against the fungus gnats in my house, and I think I've won (knock on wood). Thankfully just as I'm starting my peppers inside. Here's how I did it.
1. Inspected all house plants by shining a flashlight into them near the base. If there are gnats there they will emerge after 20 seconds or so. You'll see the larva crawling around in the soil too. I identified all the worst offenders. For me it was the plants in large pots with lots of exposed and slow-drying soil. The plants in small pots and quick-drying soil did not have any gnats.
2. I let all my plants dry out almost completely. For the larger ones this took more than a month. Thankfully none of my plants had a problem with this, but be aware some may be sensitive.
3. At the same time as I was letting them all dry out, I put the sticky pads up in all the pots to catch the gnats as they continued to hatch and took off in search of water. I replaced the pads several times as they filled up, I was amazed at how many there were!
4. Once the soil in all the pots dried out substantially and the number of gnats began to fall, I applied this insecticide to the soil:
http://www.amazon.com/gp/product/B000BX1HKI?psc=1&redirect=true&ref_=oh_aui_search_detailpage. Only use this on house plants, not anything you're going to eat (says so on the bottle). The insecticide has to be watered into the soil, and then you're supposed to wait a week for the soil and roots to soak it up and take effect.
5. Once I gave the insecticide a week to do it's magic, I removed a thin layer of the top soil in all the plants that had gnats and covered the soil in a 1/2 inch layer of sand (builders sand in some and ornamental black sand in others).
What I learned was that fungus gnats become a big problem if you are over-potting your plants and the soil stays damp for a long time. I re-potted a couple of plants after realizing this. The ones that you can't re-pot just put sand or some loose covering over the top of the soil to prevent the gnats from laying eggs. I found that my plants with mulch covering the soil did not have gnats. Also, fungus gnats seem to be a HUGE problem associated with using Miracle Gro soil, I will never use that crap again.
Good luck fighting the gnats, those suckers are tough.