For that type of work, you really want a professional workstation card (Nvidia Quadro or ATI/AMD FirePro) not the consumer cards (Nvidia GeForce or ATI/AMD Radeon).
The professional cards have certified drivers which can dramatically reduce rendering times in such applications. However, the price goes up quickly on those. Entry level workstation cards are $160ish and the next level is around $300-$400, the level above that $700ish and then you get into really expensive models. I suggest checking reviews because some people feel it's not worth buying a low-end workstation card. The complexity of things you're working on dictates how high-end you need to go.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814133354
http://www.newegg.com/Product/Product.aspx?Item=N82E16814195096