I saw where someone ask about fruit flies in a fruit storage post.  Here are some traps I made this past summer that are crazy effective.  After placing these traps in our kitchen and bathroom(they bred in our bathroom sink) All fruit flies were gone in 48 hours.

What makes these so effective is the mesh funnel.  It allows the smell of the bait,  in this case apple cider vinegar diluted 50%, to easily loft into the room.  The mesh also encourages them to travel down inside the jar.  The vinegar pickles the flies so there is no dead smell.  They are easy to clean also.  

We leave fruit and veggies out on our counter and the fruit flies prefer the traps to the real thing.  

You will need a 1 gallon paper/mesh paint strainer (from the paint store) , wide mouth mason jar with ring,  a hot glue gun,  and very sharp knife/razor blade and scissors.  

Set the strainer in the ring.  While holding it snugly, hot glue it to the ring from the bottom and allow to cool. Using the knife or razor,  cut the strainer flush with the top of the ring.  Snip the tip of the strainer making it into a funnel.  Place a cup or so of diluted apple cider vinegar into the jar and screw the lid/ funnel on.  

The smell Will draw them to it so it can be placed out of sight of you wish. I left it next to the fruit till the were under control.  

Mine hide in plain sight.  

great solution to a problem many people have Greg. Thanks for this super handy tip.

I can't remember how we did it in the genetics laboratory at university but I do remember going in one time and the lab class room was full of them, someone had knocked over all the jars our project flies were in (cabinet and all).

My fruit fly traps are similar... Stop drinking a bottle of beer when there is 1/4" of beer left in the bottle. leave it sitting out.  It will be filled with fruit flies by morning. Or leave a bit of beer, wine, vinegar in a mason jar. Put a lid on it and poke a couple holes in the lid with a knife or screw-driver. Sometimes, I might add a drop of liquid detergent to the jars.

I tried fruit fly traps like these and found that they work ok. But old fashioned flypaper worked tons better! I live in the tropics where fruit flies (called vinegar flies here) abound. With the constant influx of new flies each day, I find that flypaper does a much better job for me.

Su Ba: Fly paper works well for me also.

The traps are great ideas. They seem like a permanent solution.  Additionally, if you don't have a trap set up and need to get rid of fruit flies in minutes, try a vacuum cleaner. I take the attachment off of a canister vacuum and simply vacuum them up. I usually open a bottle of vinegar or wine to attract them and then as they get close to it, I vacuum them up.