I have a Zalman TNN500af case that I would like to add a reasonably powerful GPU (7770HD) to. I'd like the PC to be silent 90% of the time, and for the fans to either ramp up automatically when gaming, or have some sort of software option to activate them when required. I'll be using a Gigabyte GA-Z77X-UD3H motherboard. I've heard the Noctua PWM fans allow for 0rpm? Could really use someone to point me in the right direction.

Seems like you're going with the wrong motherboard. Gigabyte boards don't have the best fan controllers. ASUS and MSI offer much better BIOS and Windows controls for fan headers.

As for the cards, there are no fanless HD7770s but there are some fanless HD7750s. From what I've been able to gather, among recent value gaming cards, the GTX650 appears to have a quieter cooler than any 7770, though the nVidia card does cost more.

Thanks Mike.

The motherboard is up in the air, but the Asus motherboards I've looked at don't qualify for one of two reasons. Either there's a large MOSFET cooler above the CPU which (I believe) blocks my TNN500's heatpipes or they use this weird new motherboard mounting configuration (2 holes on top instead of 3). The Zalman doesn't allow for repositioning of the screwholes. I'll look into MSI and see what they have available. As for the GPU, I know the 7770's TDP exceeds the thermal capacity of the TTN, but with fans that ramp up while gaming I believe I'll be fine. I need the 7770 because it offers FleX Eyefinity (I use 3 monitors, mainly for productivity but want to mess with Eyefinity a bit).

Maybe mount the card as it is, without the Zalman heatpipes? Or connect the 120 mm fan to the graphics card?
The stock coolers works well fanless during 2D on new cards.
Read this thread, it seems to be a matter of picking the right graphics card.

viewtopic.php?f=19&t=65146

If I understand you correctly, then that shouldn't be a problem at all. Those motherboards would still line up with the 9 mounting holes used by ATX motherboards. They're just narrower - so they don't use the 3 holes to the right, but they line up with the other 6 holes just fine.

Compare the Asrock Z77 Extreme4 to the Extreme6 (same applies to all motherboards derived from the ATX standard):

That is a very useful illustration! I had no idea that the boards were actually narrower. That expands my options tremendously. I think my problem is solved simply by purchasing a Z77 Asus motherboard and use Fan Xpert 2 software to disable the fans when not gaming!