If you want a card suggestion, start with a budget. A relatively low-end one may not require you to upgrade your power supply. A GOOD one most certainly will.
Acceptable cards for just DDO would start in the $60 bracket. Ones you can play DDO with all the features cranked up start at around probably double that. A good new power supply will set you back maybe $70.
Personally, if I was on a budget I'd be happy with these (
I'm not in the USA, so I don't use newegg - just using the product links as an example):
Either http://www.newegg.com/Product/Produc...82E16814150485 or http://www.newegg.com/Product/Produc...82E16814102855
and
http://www.newegg.com/Product/Produc...82E16817371015
You can spend hundreds more if you want to (and get more bang out of it). And most likely, prices for those $200 cards will drop significantly over the next 6 months as new technology comes out.
If I wasn't on a tight budget, I'd get the Corsair brand for the power supply, and an NVidia GTS 450 card (brand would probably be Gigabyte or ASUS, or a higher end card - EVGA is one of a few).
Of course, if you get the parts, you need an ounce of skill and a dollop of knowledge to pull the PC apart and do the upgrades yourself, get a PC components store to install do that, or pay the right teen techie a six-pack to do it for you.