What size RAM are you looking for? This is the deciding factor. Some video cards need an extra power supply plug, some don't. What type of output are you looking for? VGA, DVI, HDMI? What are you going to connect it to, and what input does this monitor have. Are you going to plug this card into a PCI or AGP slot. What's available on the motherboard?
What output power does the power supply have? If your new video card needs the extra power plug you need to consider a larger power supply.
I've seen excellent 512 RAM cards for under a hundred bucks, standard PCI or AGP connector. I've also seen dual cards that need a dual AGP slot with a Gig or so of RAM for a grand US.
This looks interesting http://www.newegg.com/Product/Product.aspx?Item=N82E16814130534
Just curious, why is 128 Meg not acceptable?
I'm having a difficult time trying to purchase a video card, I have a stock Gateway - Desktop with Intel