The English Short-Title Catalogue, a fantastic database listing over 460,000 items published (mainly in English) between 1473 and 1800, is now available online (for free) from the British Library at http://estc.bl.uk.
In a press release, the BL notes "The ESTC is unparalleled in its depth and range containing all types of printed material including letterpress books, pamphlets, newspapers, serials, advertisements, slip-songs, election handbills and a variety of other ephemera. The coverage extends to items printed in all languages in the British Isles and beyond, to Colonial America, United States of America (1776-1800), Canada, or territories governed by Britain before 1801. It covers Portuguese printing from India, German printing from North America, Gaelic printing from Scotland, and French printing from both France and the Netherlands. It also includes false ‘Londres' imprints, for material printed surreptitiously in France and the Netherlands. Engraved music, maps and prints are excluded from the catalogue but atlases and texts which are wholly engraved are in the ESTC."
This is a wonderful resource, and I'm delighted to see it so readily available.