For those unfamiliar, the 1875 9th ed. was known as the scholar's edition due to how many eminent persons had contributed; it's a fascinating snapshot of the late 1800s.

Other material that would be fun to put online in a hyperlinked and indexed format include geographic and medical atlases and the Baedeker travel guides.

I'm looking forward to it. The 9th is great in its own right and a lot of it is in the 11th. Alfred Newton's nearly 200 articles on bird species and a few classic essays by Macaulay come to mind offhand.