Useful links:
Most incunabula can be found in the census of the British Library:
http://www.bl.uk/catalogues/istc/index.html
The best website on incunabula:
http://www.ndl.go.jp/incunabula/e/index.html
Examples of Short Title Catalogue descriptions:
http://www.kb.nl/stcn/
The best lists of references can be found here:
http://www.rarebookschool.org/
Research:
http://www.tracesofuse.eu
Handbook:
http://www.bibliopolis.nl/index/index/lang/en
Elementary but nice:
http://www.library.manchester.ac.uk/firstimpressions/
16th century French books:
http://www2.lib.virginia.edu/rmds/portfolio/gordon/index.html
