I thought I'd found my ideal board in the Asrock 890FX Deluxe5
until I realised the CMOS battery is in a really stupid (hot) place, under the VRM cooler.
What made it great for me is:
Suitable slot layout, allowing me to put my 3-slot 6950 with AXPII cooler in the PCI-E x8 slot (third from bottom), leaving a PCI slot above that for my TV tuner card, and 2 PCI-E x1 and 1 PCI-E x16. In future I could put another 3-slot card in the PCI-E x16 for Xfire and still have a free PCI-E x1 slot (I'd have to lose the PCI card for that, but I'd get a USB tuner in that case). If the PCI-E x8 and the PCI slot below it were swapped round, I could still use it as although the card would overhang the board, I'm building a custom case so could make it big enough to accommodate this, and this might actually be better, as it would leave a bigger gap between Xfire'd cards, so perhaps someone knows of a board with such a slot layout.
Realtek ALC892 audio, supporting multi-streaming.
8+2 phase power for overclocking
SATA3 and USB3 (including one front USB3 header)
Optical and Coaxial audio outputs (which I might never use, but it's nice to have both in case)
The only things I wasn't sure about is that my Corsair Vengeance DDR3 (CMZ8GX3M2A1600C9) isn't on the QVL, and whether my True Rev.C CPU heatsink with 120mm fan will fit considering the heatsinks, or will fit but block some of the RAM slots. I think this is inevitable whatever board I get though, as the only board I've seen that looks like the RAM slots have been spaced further from the CPU to avoid this is another Asrock board, the 890GX Pro3
which I'd probably get if the second PCI-E x16 was x8 rather than x4. I also think that some Asrock boards use active (ie noisy little fans) cooling, which is a big no-no.
The only other board that came close is the Gigabyte GA-990XA-UD3
but unfortunately that has Realtek ALC889 audio and doesn't support multi-streaming, which rules it out.
I also considered the Asrock 990FX Extreme3, but that's only 4+1 and doesn't have a front USB3 header (not the end of the world), and the Asrock 990FX Extreme4 has the CMOS battery in the same stupid position as the 890FX Deluxe5 (as well as all the fan headers along the top of the board!).