I don't know about you, but for me the word "clipart" has the connotation of fairly simple, cartoonish images that really are not of much use in the calligraphic world. But today I am positively swooning over the discovery of University of South Florida's Center for Instructional Technology's Clipart ETC collection!
At first glance their logo, an ampersand superimposed over a map of Florida, is a good sign--but does not even compare with the riches to come. There are 60,000 pieces of free, mostly antique black-and-white clipart, and more are being added every week. Categories include Decorative Letters (just begging to be illuminated!), Complete Alphabets, Art (including Celtic and other ornaments), Borders (corner, edge, and full page) plus vines, doodads and tailpieces. Each is offered in three JPEG or GIF sizes and a downloadable 240 dpi TIFF for printing. The database is easily searchable and will yield many treasures!
And best of all, you can use up to fifty of them in a single project without special permission if it is non-commercial or educational (and "not obscene or scandalous"---so tone it down, you wild and crazy scribes). It's a goldmine!