JSB Exacts are great pellets and are the ones that I've been using in my long range shooting - they are quite a good price too, about £4.95 a tin posted if you buy 10 tins from the Air Ammo website - their service is top notch. You can get some single tins of the different head sizes to see which one goes best in your barrel
http://www.airammo.co.uk/
Just checked the website and there is not much available though - delivery JAN/FEB 2008
You could try webley mosquito as they are much admired and used by shooters due to their light weight and good BC - bit pricey mind
The best bet is looking like the new pellet from Vernator - there's is plenty of posts about them kicking around - light weight, very good BC, great quality manufacturing and very, very impressive accuracy over short and long ranges......
Where can you get these again