There are three 'Core' books; The Player's Handbook, The Dungeon Master's Guide and The Monster Manual. Unfortunately, everyone is going to have to try and get hold of their own copies. But the SRD does have a lot of great information.
System Reference Document 3.5e
Hate to rain on your parade but PDFs of the books are illegal and probably should be removed.
Ahhh. Yeah. .___.;
Looks like everyone is on their own for this.
They're not hard to find. Going the add the D&D wiki. http://www.dandwiki.com/wiki/Main_Page
Well the core rules for 3.5 are available under the OGL, so if you're already experienced but don't want to fish through the books for a quick reference the d20 SRD works. There are a few restrictions however, such as anything that describes the process of character creation or distributing experience or anything that's part of WotC's "product identity" such as beholders and mind flayers and whatnot.
To anyone wishing to purchase legit copies of the core books or any 3.5 splatbooks, good luck to you. Wizards does not allow any chains selling 4E products to also carry 3.5 from what I hear, and they have obviously stopped production of the previous versions so there aren't any more being made.
I'd like to post more but I don't know how much of their information is protected under the OGL and how much isn't.
Phooey. All I have is the Hero Builders Guide and the older versions of Dungeons and Dragons Dungeon Masters guide and the Players Handbook. I need to update quick!