this is an excellent book, quite a few on the forum bought it when it was only £4.99 in The Works bookshop but it can still be had for not much more if you look about.
http://www.amazon.co.uk/gp/offer-lis...&condition=new my wife has put mine away somewhere and doesn't know where
I think there is around 1100 species of weeds described and there's photos on every page