Linux Server: Knox (AKA Neo3)This site, along with a number of others, is currently running on a 1U server running Mandrake Linux.
I've bought machines fully built, I've had them custom made and I've made machines up from parts myself. My first webserver was built from parts for instance, as is my home PC, and my office PC is custom built, whereas most of my Acorn kit was originally bought pre-built (apart from the fileserver which I built from spares). However the easiest solution I find is the one I took with the past couple of servers I've bought, which is to get a pre-built or custom built machine with a minimum spec to make sure it's stable and working out of the box (no worries about getting the wrong type of memory or CPU heatsink etc.), and then customize it further myself to meet my exact requirements.
The photographs are of the box as it arrived from Microland UK. The machine on the website was white IIRC, but I asked for black in the comments box when filling out the order form - they seem to be quite good at things like that. Sadly I then ripped apart their beautiful handiwork and replaced the main 40BG Maxtor drive with an IBM one - I wanted the main drive to be 7,200rpm rather than the usual 5,400rpm, I didn't know the Maxtor one was also a faster drive until I took it out. Still, IBM drives are supposed to be better than Maxtor, although personally I've never had a problem with either.
I then removed the floppy drive (because space is at a premium in a 1U case) and replaced it with a 120GB data drive - more than I currently need, but I don't intend to buy a replacement for a while; and as Mandrake recognised the onboard network interface I removed the Intel NIC and the right angle PCI adapter with an eye to using them where they're needed more or selling them on. I left the CD ROM in place disconnected simply to avoid having to make a blanking plate or mess up the cooling by having a gaping hole in the front - most of my machines either have CD ROMs already, or where possible combo DVD/CDR drives, so it wasn't a great loss.
The server also has 1GB of RAM (again, slightly overspec'ed for futureproofing) and a 1.1Gig Pentium III processor; both of my previous servers were AMD, but alas I couldn't find a cheap black 1U AMD server to fit the bill. The server is hosted in London, after power cuts trashed my previous two machines hosted under the desk at work (note to self: UPSs only last a few minutes. Proper hosting facilities have generators and stuff).
Why Mandrake?I chose Mandrake for my first server as I was building it to learn Linux. I worked at an ISP but hadn't been taught much server-side stuff - I knew only a few Unix commands from my days at Uni, and as I didn't spend a great deal of time at Uni that wasn't much. I waited until the boss was in America for two weeks and decided to jump in at the deep end, building my own machine, installing Linux, getting it up and running and then seeing if it would stand up to life on the Internet. Not being a complete masochist I did quiet a bit of research and Mandrake was gaining a reputation for being the easiest to install at the time, while being Red Hat compatible in case I had problems finding updates. Some people seem to have a problem with an easy to install Linux distro, tending to dismiss Mandrake in favour of "real" flavours such as Red Hat or SuSE, but I'm running the same services as I would on any other distro and I've not had any problems with it so I've seen no reason to change, simple as that.
 I bought my home PC motherboard and forgot the header card required to give 5.1 surround sound, and when ordering the card I asked for the order to be combined to save postage - which amazingly they did!