Nature has been quite ingenious. Why not take advantage and see just how effective carnivorous plants can be! For large houseflies and blue bottles you can't beat Trumpet pitchers (Sarracenia). They do need full sun though but if you don't have that, try a large Monkey Cup - Nepenthes x ventrata is excellent.
Small flies such as fruit flies and compost flies will get caught by the Sundews (Drosera) - sun loving plants, but if you have a north facing windowsill try a Butterwort (Pinguicula).
Butterworts are also excellent at catching whitefly in the greenhouse or orchid house. Place underneath the foliage of other plants to keep out of the full sun.