I always go with nVidia, and they haven't given me anything to complain about yet.
I've got a Winfast Geforce4 128mb Ti4200 VIVO. I'ts pretty sweet and only set me back about $400 Australian. It's got dual monitor support, TV out and even a video capture function as well! Everything works alright and I find it fine with Maya. It's also great for playing high-end 3D games.
What sort of card you should get depends upon what you are wanting to do with it.
REMEMBER: graphics speed is not only determined by your video card, but also by your CPU and RAM. For example... if you have a Pentium 200Mhz with 64mb of RAM, then buying a top of the range video card will do almost nothing (not to mention the hardware compatability issues).
Hope this helps ya a bit mate
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