There is work on an open source driver (Lima git) for the Mali GPU that is used in all recent Exynos versions.
ARM is working on a unified KMS driver structure for most ARM SoC that will handle modesetting and 2D with an X component. Then load a binary blob to drive proprietary parts, such as their Mali GPU. An approch they borrowed from OMAP.
An open source frame buffer driver for Tegra2 chips shows up on the dri-devel mailing list. As of 3.6-rc1 the source is not yet in the mainline linux kernel though there appear to be plans for future inclusion.
There was a driver from Qualcomm, but it doesn't seem to have advanced anywhere.
Texas Instruments (OMAP)
A KMS driver for simple modesetting is included in the staging area of the kernel since version 3.2. This driver does not provide 3D support though there may be plans to add support for loading a binary blob. There is also an X driver (git).
Atom SoC with PowerVR graphics.
We will find out soon.