There are lots of internet places you can visit to learn more about George Lippard and his works. You can now follow George and all announcements for the George Lippard Society on Twitter. George also has a page on Facebook.
Years ago I began a Lippard site on which I was going to re-serialize The Quaker City, with annotations. That project fell by the wayside (although I've always intended to revisit it):
The Library Company of Philadelphia's exhibition Philadelphia Gothic has lots of images and info about Lippard as well as a pdf guide for research:
The Literary Gothic has a page on Lippard with links.
The Wikipedia page on Lippard seems well-maintained.
From the Baltimore Society's Edgar Allan Poe site:
Emilio De Grazia, "Poe's Devoted Democrat, George Lippard,"from Poe Studies, vol. VI, no. 1, June 1973, pp. 6-8
Burton R. Pollin, " More on Lippard and Poe," from Poe Studies, vol. VII, no. 1, June 1974, pp. 22-23
Lippard's works online:
Christopher Looby has put online some of Lippard's early pieces from The Spirit of the Times and The Citizen Soldier newspapers: The Early Writings of George Lippard
The Quaker City or the Monks of Monk Hall at the Internet Archive (read online or download pdf)
The Life and Choice Writings of George Lippard(includes a bio by John Bell Bouton)
Internet Archive full list of Lippard's works available online (including, Blanche of Brandywine, Washington and his Generals, Washington and his Men, Legends of Mexico, The Nazarene, New York: its Upper Ten and Lower Million and The Mysteries of Florence)
Open Library has a list of Lippard's works, some of which you can read online.
If anyone else knows of any other Lippard resources on the internet, please let me know.