Can anyone recommend a suitable hard disc for backing up the files my Mac. The Apple time capsules are £200 odd. I presume there's something a bit cheaper than that that would do the job just as well?

Time machine, and any external disk, ideally on your home network if you have one, but a standalone external drive can be used.

Any brand, or do they vary in quality? I'd look on Amazon by default unless there are better places to get one from.

£200 for an external disk drive?

i am using some cheap hard-drive i got a PC world to back up the SOs laptop. The only downside is that it isn't wireless so i have to plug it in once in a while.

I've got a 1TB iomega that I use- only downside is that it's big, noisy and needs it's own power socket. If buying now, I'd get something like a Western Digital Passport which is small, light and quiet, and gets it's power from the usb socket- it's less annoying keeping it plugged in all the time so Time Machine can access it when it wants.

The point of a time capsule is backing up over wifi, instead of having a house brick plugged in all the time.
You can use any NAS drive & a wifi router, but they might not play with time machine.
Time capsule is also a wifi router. Western Digital do Mac edition HDs, fire wire if you want to use that.

I have the 750gb version of this one

http://store.apple.com/uk/product/TS585ZM/A?fnode=MTY1NDA0Nw&mco=ODE0Mjk0Nw

it can be noisy but small price to pay, firewire connection and it works as a usb hub too.

The most important question is surely, "does any one make an alternative that looks ac cool?"

I used the instructions in the pdf downloadable from here

Works fine over wireless and most of the instructions aren't qnap specific. Key step is to enable unsupported volumes in timemachine.

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

In theory that should allow any share to act as a timemachine volume.