First go looking through your owners manual and papers, a lot of times your card with your radio code is in there or the dealer wrote it inside your owners manual.
If not, and you do not know how to pull the radio out yourself then go to your local Circuit City (if they are anything like the one where I install at they wont charge you) and ask them to pull the radio out and get the serial number off the top of the radio.
Take that serial number and contact honda and ask for the radio code, you may have to go there and provide proof of ownership before they will give it to you.
Also please use the search feature. This has been covered plenty of times already.
Going to make this a sticky.
<~~ HCF Security Guard