I don't use batteries and I really hate the switched power sockets we often use, they take up too much room, the metal nuts are often poor quality, and I don't like having to drill 12mm holes if I don't have to. So I've been using the none switched versions from JPR Electronics, but they were around 50p each.
Just bought 100 off this seller though, 18p each seems much better to me! These are really highly recommended if you're not bothered about batteries and they seem much less hit or miss than the larger switched versions:
http://www.ebay.co.uk/itm/321133081014They only need an 8mm hole which is much nicer