PDroid is a free Android utility that allows you to see and block access by apps on your rooted Android phone to your personal data and individually identifying information. The tool shows you which apps have access to information like your phone number, your Device ID (IMEI/MEID/ESN), SIM serial number and lets you disable access without breaking the apps in question.
Keep in mind this is different than blocking intrusive permissions to hardware or other apps, like previously mentioned LBE Privacy Guard or Lookout does. Apps that want access to your personal data won't break if they can't get it and more importantly they can't send that information back to the publisher or developer if they don't have access to it either.
PDroid is available for free in the Android Market. Head over to the XDA-developers forum link below for a full list of the information PDroid keeps private after it's installed.