If you get a DX9 card now you can't use DX10 until you upgraded in the future. This isn't a huge problem, because most new games know the devastating price of a DX10 card and are compatible with DX9, and all games made before January are DX9.
I'd recommend the EVGA 7600GT. Its cheap at only ~90-100 dollars and EVGA is a trusted brand. Also, the 7600GT will be able to run most games are high settings (I run CS:Source at max settings). I don't know how much gaming you do, but it will do the trick for now.
In the future (maybe a year?), you might want to buy a DX10 card, and they will be much cheaper. I know some of the ATI DX10 cards will be originally listed at about 235 dollars.