Here's a link to my original post recommending EON2's :-
http://www.ukgser.com/forums/showthread.php?t=38820&highlight=eon2+spark+plugs
I changed them at 40K - but they were still running great and could have stayed in a lot longer, but I still had two plugs from the original pack of four from Halfords.
I know Straypuss was supplying them for a while but this has now stopped. however, I recently ordered a spare pair from this site:-
http://www.spark-plugs.co.uk/index.htm
At £3.50 each there a hell of a lot cheaper than Halfords ( £19:50ish for 4) and they supply them as singles - so you can order just 2

. I ordered mine along with a few more plugs for the car and other bike so postage is less of an issue - delivery also excellent.
Still reckon these plugs are the business.
Cheers..................Grizzly