Here's a cool page about Hebraica & Judaica Incunabula.

And here's a decent definition of the term Incunabula: The printing art was at the time of its inception as revolutionary an achievement in human history as computer technology in our own day: it is referred to in Hebrew sources as a "heavenly craft." Books published in the earliest period of printing, from the time Gutenberg introduced printing to Europe (ca. 1455) until the year 1500, are known as incunabula, or cradle-books. (taken from a page at the above exhibit)