If I wanted to be rich, I'd invent and market a Personal Sound De-Amplifier. It would be kind of like the Listen Up Personal Sound Amplifier. If you haven't seen the commercials for this, check out their website. The device allows you to eavesdrop on your neighbors while pretending to check your mail, among other things. Anyway, my device would have the opposite effect, allowing you to selectively stifle annoying sounds in your general milieu. Ideally my invention would work with a remote that you could point at people and things to turn down their decibel level. I can think of the following uses for such a device:

• Drown out HPGs (High Pitched Gigglers). One of these is sitting two tables away in the coffee shop where I am currently working and does not seem to want to tone down her supersonic laugh, despite my dirty looks.
  
• Stifle the LTs (Loud Talkers). The male half of a couple playing backgammon today was an LT and did not seem to knotice that the entire coffee shop could hear his game.
  
• Reduce outdoor mowing/weedwhacking sounds, which seem to occur only on the days I want to sleep in.
  
• Turn down the volume on passing trucks and cars when you are trying to talk on your cellphone outside.
  
• Turn down the volume on annoying cellphone talkers

It's a pretty self-centered device, really. So I think it would have a pretty good market.