Copac

Because I've been immersed in research over the last few months I've become increasingly aware that one of the websites that I use more than any other is Copac. For those who don't know Copac - it is the "merged online catalogue of major University and National Libraries in the UK and Ireland", and a fantastic resource for identifying and locating books. Now it has become even more useful with the trial introduction of a search interface enabling users to simultaneously search Copac and the English Short Title Catalogue (ESTC) of materials published between c1473 and 1800:

www.copac.ac.uk/