For me it's tricky. I've gotten myself down to one PC; from 4 primary machines (gaming, silent office, file/print/VM server, HTPC). Because of this, I need to do a lot of stuff. Here is what I plan on sticking in it:
Modified P180 (ducted, multi-chamber airflow)
Antec NeoHE 480W (might need bigger?)
4x Scythe S-Flex FDB 120mm fans @ 800RPM (nearly silent)
3x 750GB Seagate SATA (JBOD - backup on another machine)
1x 74GB Raptor SATA (Dual-boot Server 2003 Standard R2 and Vista Ultimate)
1x 2GB Sandisk Ultra II on CF-IDE adapter (for Vista caching goodness)
3x Samsung DVD-RW drives (identical, for ripping stuff)
4x 1GB DDR2-800 (2GB DIMMs are still too pricey)
AMD X2 5400+ (2.8Ghz)
XFX 7950GT Fanless (driving 2 Viewsonic VP2130b LCDs)
XFX 7600GS Fanless (driving Samsung 191T LCD and Sharp XR-20X projector)
Auzentech X-Plosion 7.1 Soundcard (SPDIF out to receiver - thanks Merc)
MyHD PCI HDTV Tuner/Decoder MDP-130 (looks decent, haven't tried it yet)
I'd like to have the extra space between the 7600GS (middle PCIe) and the soundcard (top PCI) to work some of my ducted goodness