I mostly do network administration, with a bit of gaming in my off hours. I do a little image editing and video on this. It's also my primary audio source.
I added a second 256 SSD so I can do RAID 0 because the added capacity is nice as well as being able to utilize the throughput of both 6 Gbps channels at once.
I'm running Polk Audio Monitor 30 Series II speakers and a Polk PSW10 subwoofer off an old Denon 80 watt/channel receiver.
I just added a second GTX 560 Ti and configured SLI as well as a third monitor. I was temporarily not able to use my Asus Xonar ST until I located a longer SLI cable. This required me to relocate the second video card to an 8x PCIe slot, but apparently that makes almost no difference in speed.
I should also say that a fair chunk of these parts were cannibalized from my last machine (rotational hard drives, optical drives, sound card, keyboard and mouse, and one of the monitors).
I added another 16 gigs of low profile Vengeance RAM, which shouldn't have made a significant difference, but does. I guess I can attribute it to running legitimately quad channel RAM as this mobo is supposed to.