My son and I have been spec'ing things out for an HTPC low-profile system. To us it appears the 4350 and 4550 cards have similar processing power, etc, although neither has the power to do high-end graphics. So look at the 4350 since you can't find a 4550 card. Check at XFX here for fanless (heatsink only):http://www.xfxforce.com/en-us/products/graphiccards/HD%204000series/4350.aspx
There are 3 versions; the lower two have HDMI outputs and either 512 MB or 1 GB DDR2.
These cards are all low-profile with standard-profile end brackets, but they come with a low-profile replacement bracket for conversion. It is not clear to me, though, where the D-dub (for VGA) goes when you do that conversion. You either mount it on a second plate (included or not unclear?) or just forget it.