Some years ago, I worked on a wordless comics bibliography - "Stories Without Words : A Bibliography with Annotations" compiled by Michael Rhode, Tom Furtwangler, and David Wybenga, International Journal of Comic Art,v. 2, no. 2 (Fall 2000), p. 265-306.
David Berona's done more than anyone else to bring some forgotten works back to public view. Here's a profile of him: "Central alum writes the book on wordless books; David Berona links wordless books of '30s to today's graphic novels," By Andrew McGinn, Springfield News Sun Thursday, July 24, 2008.
Needless to say, the bibliography's out of date. Lio's my current favorite wordless comic strip.