A few years back we moved into a nice little house that had one problem. Apparently, the previous residents were kind of slobbish. The house had a bit of a roach problem. We tried different products, sprays, foggers, etc.
Before I go any further, let me tell you my way of thinking regarding pest control. It's basically this: Why use a flyswatter when a tank works even better?
With that said, I wanted to find something so strong that I probably shouldn't be using it. We had a professional scheduled to come the very next day when I thought "there must be SOMETHING out there I can use to do this myself". So, $50 in hand I went to our local Wal-Mart in search of something deadly.
I finally found some of this. It's Bengal Concentrated spray. Browsing the page you'll see Recommended for commercial and industrial use... PERFECT! I link to Amazon because I haven't been able to find this stuff at Wal-Mart recently. Anyhow...
This stuff is absolutely the shit. Combined with a cheap/decent one gallon sprayer you're good to go.
The concentrate is... well... highly concentrated. You mix it with water in one of two mixtures. For a light infestation or just maintenance after you've sprayed before, mix one half of a vial of concentrate to one gallon of water. For a heavy infestation or if you just prefer the "nuke them from orbit, only way to be sure" approach mix one whole vial to one gallon of water.
Remove any children or pets from the room and spray every crack, cleft, corner, cranny and crevice with the stuff. Once the room is completely dry, the children/pets can safely re-enter. Do this for every room, hallway and closet in the house. It may also be useful to go around the perimeter of the house, around windows, doorways and such.
If your problem is specifically roaches then, once the area is dry, you might want to lay down some roach bait to get any survivors. I find the Gel stuff to be easy to work with and it'll stay where ever you put it.
This worked wonderfully for us, it just eradicated the fuckers. Like I said at the start of this post, I'm not exterminator. Try this at your own risk, I'm not responsible for what happens. I can only tell you that it worked for us and I'll definitely be using bengal concentrate from now on for pest control.