Valancourt Books: James Jenkins and the folks at Valancourt have produced wonderful editions of many rare 18th- and 19th-century novels. You won't find many of these titles anywhere else. Their offerings are especially strong in Gothic fiction and novels of the 1890s.
Broadview Press: Broadview also has strong offerings in fiction of the 18th and 19th centuries. If you like in-depth scholarly introductions and lots of notes and appendices, Broadview provides a lot for the money.