|Integrated NVIDIA® GeForce® 7100 graphics solution|
PCI Express® x16 graphics card support
That from the ACER website.
Since the board is based on NVIDIA chipset you would be best advised to stick with an NVIDIA based PCIe graphics card.
You will also need to upgrade the powersupply if you wish to install any PCIe card since the original powersupply is only 300W. As to which card is best? Decide your budget and factor in at least $50 to $80 for a new powersupply. Cards can cost sub $100 or over $1000. Define your needs and budget.
Goin' Fishin' (Some day)