Mid 90's, there was this:
http://www.amazon.com/Library-The-Fu.../dp/B00002S8OW
Also a variety of PD CDs with the Gutenberg collection.
Around the turn of the century, a lot of Universities hosted their own digital libraries of classic literature. The University of Virginia partnered with Microsoft to produce very high quality digital editions for free. Around that time came the now legendary BLACK MASK collection you could d/l for free or buy on CD in the format of your choice; LIT, MOBI, PDF, HTML, or ROCKETREADER. I got all, of course. Repeatedly.
Amazon and B&N sold contemporary titles in Lit and pdf, Powells, too--availability was hit and miss, prices often outrageous. B&N ditched early, Amazon soldiered on until they started preliminary work on what became Kindle.
The primary source for contemporary fiction through the 90's and early 21st was USENET: the demand was there, supply wasn't, so the underground stepped up. Lots of legends floating around from those days. Occasionally a "pirate" would surface to give an anonymous interview and swear they would happily stop if only the publishers would make the titles available. Even then the mantra was "Look at BAEN!".
I remember walking into a CompUSA (original chain) to look at the first CASIO color PocketPC and the store demo had a pristine copy of LORD OF THE RINGS in MS READER. When I asked the employee where you could get it, he took it away and said it was just a demo. Of course, I already knew it was a full copy so it didn't take much to figure out why he was spooked.
You needed to think like a scavenger in those days and it helped to be familiar with ALTAVISTA. It once coughed up for me an argentine university etext library of 19th century latinamerican fiction organized by country and author. No downloads but each title was a single scrolling page of nicely formatted HTML. Took me a few nights (via dialup) to screenscrape them and a week to convert to LIT and Mobi.
Amazon changed all that.