Asus 3 port video card

The lowest Radeon card that can do EyeFinity (3 monitors) is the HD 5570. However, not all Radeon HD 5xxx cards below the HD 5750 supports EyeFinity so verify before buying.

Here's an example of a HD 5570 that supports EyeFinity.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814102875&nm_mc=OTC-Froogle&cm_mmc=OTC-Froogle-_-Video+Cards-_-Sapphire+Tech-_-14102875

If you already have the HD 5450 and you have another PCI-e slot, then just buy another HD 5450 and connect the 3rd monitor to it. Otherwise buy the HD 5570.