Cheapest way to get a new CD key

What's the cheapest way to get a new CD key? I don't want to bother buying the box and CD, since I already have the full client installed - I just need a key to add on to an account.

The legal way

Well, I once bought just CD key online . First they claim my card is suspicious, got my money but sent nothing. Loooong time to get through support "sytem" to get number to call and then loooooong call to support with someone who really need to learn a bit more English. I am non-native English speaker and my level of tolerance is quite high, but the lady really was not comprehensible. Loud music playing on background didn't help either. Then I got photo of my new CD ... hurray .... just to find out it was unreadable. Than more loooooooong calls...

Long story short - buy a box or buy in official online shop. Unless of course you want your adventures start even before you create your character;)

NCSoft store, or from a reputable online retailer. If you go for the retailer just put the box in a recycling bin or something.

You can buy from NCSoft, Steam or http://www.direct2drive.com , all of whom give you the game without sending a box.