I have been looking for an app that shows signal strength in DB's, since this is much more accurate. If you have a DB of around -70 you have just about a perfect connection. Around -100 and it will probably get dropped. This app is called Real Signal. It puts two strength indicators in the notification area, one green for phone and red for data. They are 5 bar indicators which are pretty accurage. The dev gives the bar ratings in the setup page.
To see your actual DB strength, you simply pull the green bar down into your home page and the db strength is indicated.
The app is currently free. I have sent an email to the dev asking him to develop the app to allow users to have a choice of the 5 bar graph in the notification area or an actual DB readout. Awaiting reply.
Let me know if anyone is using this app and finding it useful.