|Why do you insist on DDR? Don't confuse the motherboard RAM & the video card memory, they have nothing to do with each other. If your board has DDR RAM, it doesn't matter if the video card uses SDR, DDR, DDR2, DDR3, etc.|
AGP cards with DDR memory are older/slower cards & I highly doubt you'll find one that supports HDMI. What exactly is the upgrade for? Gaming? Home Theater? Are you sure you power supply can handle the added load?
Here's a Radeon HD 4650 AGP card with 1GB of 128-bit DDR2 memory for under $75 after rebate. It has one VGA, one DVI & one HDMI but it requires a 6-pin PCIe power plug: