This comes up nearly every week in one form or another, so I will refer you to some older links that have good general advise, and links to specific wire.
It is the general consensus that you buy
speaker wire and not common lamp cord. Even low cost
Speaker wire has a higher quality copper than lamp cord. Usually, with Speaker wire, you will see some reference to
'oxygen free'.
Next, keep all your cables and wires in proportion to your equipment. In other words don't spend £200 on an amp and £300 on speaker wire.
An extension of this, is that for the average consumer, any wire over £2 per meter is overkill. Wire in the £1 to £2 is more than enough for anyone. Now, if you have several thousand into your equipment, what is a few hundred more for speaker wire, but that is a level of luxury few of us can afford.
In terms of wire size, for most users with short runs, wire that is rated at 1.50mm² or AWG 16ga is fine. This is the most common general purpose wire with substantial power reserve.
For those wishing a little extra, 2.50mm² or AWG 14ga is also very common and excellent for high powered amps or longer runs.
A few individuals will buy 4.0mm² wire, which is overkill in my opinion, unless you have amps with several hundred watts per channel, or exceptionally low impedance speakers.
For a vast majority of consumers 1.5mm² or 2.5mm² is more than enough.
So, here are a few links that will in turn link to other sources of actual wire -
http://www.avforums.com/forums/speakers/915644-speaker-cable-tannoy-f1s-ca-a5.html
http://www.avforums.com/forums/speakers/919759-qed-micro-wire.html
The link listed are links I found by searching the Internet, I've not personally done business with these companies.
Steve/bluewizard
