The Abraham Lincoln Paper Collection at the Library of Congress is both a fascinating collection and an interesting digitizaiton project. The LOC's complete Lincoln paper collection consists of 20,000 seperate documents. The digitized part of the collection is a result of a collaboration between the LOC's Manuscript Division and the Lincoln Studies Center at Knox College. Altogether the digital collection includes about 61,000 images and 10,000 transcriptions. Each of these 61,000 images exists as a jpeg, a gif, and a tiff. The tiff masters were transferred to the National Digital Library Program (NDLP). The archival gif versions, however, are freely accessible online. The site design is very basic, and looks date. According to the homepage, the site was last updated March 21, 2002. I'm certain that the site is actively maintained, but the collection does not appear to be engagingly curated.
Before existing in a digital format, the Lincoln papers were captured on microfilm. The index created for this microfilm collection served as the backbone for the organization of the digital collection. The papers may be searched by keyword, or by textual content. It is also possible to browse the collection based on date. Upon retrieving an item, metadata is provided in the form of date, subject, to whom a paper was written (if it is correspondence), and series. The files enlarge very nicely so that you can really see all of the detail in the handwriting. This is a really superb collection, and is no doubt of great interest to historians, biographers, and other sorts of detail-oriented researchers.