I've had my iphone since December 2008 and I've charged it through my computer, through a wall outlet and in my car with no problem. Last night, I went to charge it and though I get power to it, it doesn't charge. I've tried it through my computer and through the wall. No luck.
Try rebooting the phone. Try a different cable. Have your tried both the Apple charge and your computer? If you are using a dock try connecting directly to the cable. Last resort, take it to an Apple store or call iphone support.