ESANN Electronic Proceedings - Free access to proceedings of past ESANN conferences in PDF format. Some abstracts are missing and some papers are scanned. - http://www.dice.ucl.ac.be/esann/proceedings/electronicproceedings.htm
NIPS Online Abstracts and Papers - Free access to papers for all NIPS conferences. Papers are in DjVu format (free software and plug-ins available). - http://nips.djvuzone.org/