In recent months there's been the new Poulsbo DRM driver from Alan Cox that has improved the open-source driver situation for the Intel Atom SoCs with graphics cores derived from the PowerVR technology at Imagination.
This new open-source driver doesn't support hardware acceleration, but at least provides kernel mode-setting and aims to provide a bit better open-source "out of the box" experience for those stuck with this poorly-supported hardware.
CompuLab Fit-PC2 with its Intel Atom Z530 Poulsbo processor. I was running this hardware as one of the comparison systems in the 12-core ARM benchmarks. Early on in the Ubuntu 12.04 cycle when last running this Poulsbo hardware, I found Poulsbo Looks Better On Ubuntu 12.04, But Still Ugly. Unfortunately, it's regressed in the past half-year.
Intel Valley View where we will have a next-generation low-power Atom SoC with Ivy Bridge graphics. Rather than the PowerVR mess it's very nice in-house IVB graphics backed by the proper Intel open-source Linux graphics driver.