If you’re looking for an inexpensive Linux box, you’d probably find it hard to beat the low-end Mac Mini. It currently goes for £399 in a configuration including a 1.83 GHz Core 2 Duo, 1 GiB of RAM, an 80 GB hard disk, a CD-RW/DVD-ROM drive, both VGA and DVI output, a remote control, gigabit ethernet, 802.11b/g wireless, Bluetooth, Firewire, four USB ports. The case is only 51×165×165 mm, and the system’s all but silent.
Picking up a non-Apple keyboard, optical wheelmouse, and 17” or 19” DVI monitor will take the total price to somewhere in the region of £500–£550. What’s not to like?
If you’re looking to run Mac OS, you can still go with the non-Apple monitor and mouse, but you’re probably better spending the extra money for an Apple keyboard; OS X is somewhat confusing on a standard PC keyboard. But if you’re looking for a desktop system, note that the more extra bits and pieces you buy, the closer the price will come to that of an iMac, at £799, especially if you go for the high-end Mini at £499.
Update, 1 Oct: Well, there are two caveats if you want to run Linux, it turns out.
First, the system won’t boot up without a monitor plugged in. (That particularly annoyed me given that I bought mine to run headless.) Googling reveals some workarounds, including a VGA connector with a resistor soldered across two of the wires, or a £20 third-party dongle that pretends to be a monitor for DDC/EDID purposes.
Second, current Linux kernels seem to have some issues with the ethernet chip, at least using the sky2 driver: occasionally (perhaps once a week or so on average) the network connection drops, and can be restored by unplugging and replugging the ethernet cable. However, I’ve had similar issues with the sky2-driven ethernet chip in my laptop, and they’ve been resolved by kernel updates, so I don’t expect this situation to last forever.