I've just finished Timothy Keller's book Counterfeit Gods. Great book... I recommend you read it.
I started reading Keller's book with my imagined image of Old Testament idols in my mind's eye. I'm picturing people bowing down to something that looks like those massive Easter Island statues. And your response, if it's similar to mine, would be: "Those misguided, foolish Old Testament people!" But aren't we just more sophisticated idolaters? And we're no less misguided or foolish. I believe that idolatry remains a significant spiritual problem (maybe that's why it's the first commandment of ten) for those of us who live in the year 2010.
In the beginning, God created us in His image. We've been creating Him in our image ever since. Instead of worshiping the Creator, we settle for something less. We create substitute, counterfeit gods (that's with a small g). And here's the insidious way these idols become idols. Most idols are good things, but those good things become bad things when we position them ahead of God in our lives. Instead of being the the great I AM, God become a means to an end. We want these idols more than we want God.
So how do we identify an idol? I'd suggest four idol identifiers (feel free to add others to the list):
1) What consumes your thoughts? Your daydreams are idol clues. If it's something you think about more than God then it may be an idol.
2) What bad habits do you struggle with? Your addictions are idol clues. An idol is something you cannot control. It controls you.
3) What do you spend too much money on? Your spending habits are idol clues. Where your treasure is, there will your heart be also.
4) What produces your strongest emotions? Your intense emotions are idol clues. If you want to identify an idol, all you have to do is identify your emotional attachments.
Identifying an idol requires a willingness to be brutally honest with ourselves about ourselves. If anything becomes more fundamental to our happiness, meaning in life, and identity... then it is an idol. And the only way to free ourselves from the destructive influence of counterfeit gods is to turn back to the true One.