In the world of graphics you are usually stuck with x16 mechanical (and electrical) add in boards for your GPU love. This makes it a little rough on many an HTPC builder. Sure you can get a half-height card and even ones with an extra tang for the low profile cases but unless you want to shell out a ton of cash you are still getting an x16 card.
Thankfully, that all may be changing; HIS and Club3D are offering x1 PCI-e cards that won't break the bank.
HIS is offering an ATi Radeon HD 4350 with 512MB DDR2 (Core clock 600MHz Memory Clock 800MHz). The 4350 is a great card for and HTPC or for anyone looking to run just business graphics and features DVI and HDMI out as well as the typical VGA. If you go half height you still get to keep HDMI and DVI.
From Club3D we find an offering from the green team. This is the 8400 GS, again another card with a small foot print in terms of usage. It does not feature an HDMI port only DVI and TV. It also only has 256MB of memory. The benefit to the 8400 GS is passive cooling.
As far as choices between these two the HIS 4350 is better for an HTPC but the 8400 GS can keep your rig quieter. Both cards seem tailor made for the Atom platform as many existing ITX Atom system boards only have a PCI-e x1 slot. A couple of dollars in this area can get you some extra horse power in any Atom Based Nettop or HTPC.