Project Gutenburg, perhaps the most important online book resource out there. This group has digitized thousands of older (i.e. copywrite expired) texts. http://promo.net/pg/
This slashdot topic covers various re-distributions of PG - to things like HTML. http://slashdot.org/article.pl?sid=04/05/24/115222&mode=thread&tid=146&tid=188&tid=192&tid=99