http://imxcommunity.org/ you can do searches on these and they are VERY helpful.
The i.mx53 Quick Start board will only do 1 HDMI output with an add on board but the base board as mentioned previously is $150.
The i.MX6 processor series is very new at the moment and they don't have a quick start board. The one I listed is a Development board from another company that costs about $300 but has the HDMI port already built in.
BOTH boards are ARM based but the difference is the 53 has been out a lot longer and has drivers available for a lot of things. The 6 series can be hard to get a hold of drivers for because it is so new still. BOTH boards come with Ubuntu but you can download Android 4.02 or WinCE7 for them. The source for Android and Ubuntu I believe are free due to their licensing but with the WinCE7 you have to purchase the source code if you want to change what base options the OS loads with. Trimming the OS's in any of these versions is the trick once you have your setup done. If you are doing a simple CarPC with this I would doubt seriously you would want to mess with the source at all unless you are adding drivers for some device.
Sorry if I duplicated any information I already mentioned. The Via or a Atom based board would be cool to play around with at the size of the PI. The intel NEXT board will be nice since it will be able to run standard windows on a computer not much bigger than a credit card.