elibsrv
a light OPDS/HTML server indexing EPUB and PDF files
...It's worth noting that elibsrv is a complete solution - ie. it doesn't rely on third party software (most similar solutions are designed to work with Calibre...). Requires only PHP with sqlite.
If you'd like to see how it looks for real, feel free to test on my 'demo' server (contains a few public domain books) - you can test it both using a web browser and an OPDS device:
http://elibsrv-demo.viste.fr