Sites are listed alphabetically by last name of collection / writer(s). Click the accompanying picture to access the main website under discussion.
The Adams Family Collection
Letters date: collection as whole spans 1639 to 1889
The Massachusetts Historical Society has a FABULOUS site offering all the diaries and letters of Abigail Adams (my favorite among the group), John Adams, and their family.
The Boswell Collection
Letters date: 18th-19th century
Beinecke Library’s FABULOUS site features images of Yale’s extensive Boswell Collection.
The Browning Letters
Letters date: 1830s-1880s
Like Yale (Boswell, above) Baylor University offers online their “unparalleled collection” of letters to and from Robert Browning and Elizabeth Barrett Browning. Even worthy of a “Flicks Picks” entry.
Leigh family papers
Letters date: 17th to 19th century
From Huntington Library’s acquisition of the “Leigh Papers” (related to Jane Austen) is fully digitized.
letters of Sophia Robertson
Walter Scott correspondence
Letters cover: 1787-1832
E-text site; Grierson’s volumes (without the notes) form the basis of this site.
The Millgate Union Catalogue, though without letter text, is “the” site for seeking information about correspondence to & from Scott.
William Henry Fox Talbot correspondence
Letters cover: 1800-1877
Philip William’s letters
Letters cover: 1760-1790
Formed the basis of Barry Shurlock’s book The Speaker’s Chaplain & the Master’s Daughter (NB: I got my copy via mail from P&G Wells, Winchester, England)