One I've been using lately aside from the ones mentioned above is http://www.velomax.co.uk. The site is a bit naff but has a good range of lengths. They are the ACI Alpina ones, double butted with brass nipples. 27p each at the last count. Postage is about £2.00 and they get sent out quickly. Cyclebasket charge £6.00 postage as they use a courier, so only order from them if you are getting other stuff rather than just spokes.
One I've been using lately aside from the ones mentioned above is http://www.velomax.co.uk. The site is a bit naff but has a good range of lengths. They are the ACI Alpina ones, double butted with brass nipples. 27p each at the last count. Postage is about £2.00 and they get sent out quickly. Cyclebasket charge £6.00 postage as they use a courier, so only order from them if you are getting other stuff rather than just spokes.