Whether it's on purpose or by accident, companies often slip charges into your bills for things you didn't ask for, and learning to spot them can save you big bucks.
Your credit card bill is fertile ground for pricey errors. Scrutinize your bills for charges you don't recognize, and be ready to send written notice to your credit card company if you find one. Credit card companies can't report a charge as delinquent for at least 60 days if you've disputed it in writing.
Medical bills can also be riddled with errors. An error in coding in a treatment or service can result in big bills and an empty medical savings account, so be sure to look over statements from your insurance company and medical provider to be sure you're only being charged for services you got.
Lastly, phone bills are notorious for including excess charges, often in small amounts that may fly under the radar, so keep an eye out for charges for Internet connections you're not using, additional voice mail services, Web hosting and other services you never ordered.