I don't know if this stuff is still available on the Wizards site or not, but there were quite a few 3.5 articles that fleshed out different parts of Eberron, with most if not all of them being written by Keith Baker himself.
I remember articles on the Daughters of Sora Kell, Zilargo, the Mournlands, kalashtar, druidic sects, and more.
Here is the link to the 3.5 Eberron archives. I can get into it, but that's not to say everyone might necessarily be able to. I'm not sure how much might be behind the DDI wall (if any). But if you want more Eberron fluff, here it is.
Eberron Archive
I would also be remiss if I did not plug this absolutely fantastic document that a guy on the Wizards.com community forums created and posted... which is rightly called the 'Revised Grand History of Eberron'. It basically takes timeline fluff from almost all the Eberron sources and compiles them into one single historical document timeline. Fantastic reading in my opinion. Here's the thread to find the document.
Revised Grand History Of Eberron!
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