Eighteenth Century Collections Online
Offers full-text access to English-language titles and editions published between 1701 and 1800 including books, pamphlets, almanacs, and treatises. Subjects covered include history, geography, fine arts, medicine, science, literature, language, religion, philosophy and law.
Titles from ECCO appear in Tripod's Books and More. Look for the subject division "Early Works to 1800" in the filters next to the results list. You can further refine titles by limiting to publication dates in the 1700s.