Are there any good official resources (racial feats or class substitutions) for Lizardfolk characters in 3.5? Races of Eberron threw goblinoids and orcs a bone but nothing for the poor denizens of Q'barra. I'll be playing in Eberron but non-setting specific resources are fine. I don't imagine there's much but there's gotta be something and I'm having no luck finding anything.
Beyond BESW's answer of Savage Species and Serpent Kingdoms containing mechanics that can be employed by lizardfolk but aren't exclusive to them
There's Very Little
Few attempts were made to make Dungeons and Dragons, 3rd Edition lizardfolk interesting, which is kind of a shame, really, for an iconic creature with over 30 years of history.1
I am unaware of any lizardfolk racial substitution levels published by Wizards of the Coast.
The "Serpent Kingdoms" book (early 3.5, with lots of 3.0 relics) has some features for lizardy folks. It's poorly laid out so it's hard to be sure, but I don't see anything specifically for lizardfolk; instead it's got options for "Scaled Ones," which is a generic term for sapient serpenty peoples including lizardfolk. Mostly it's got a handful of feats, but there are also some amusing equipment options for Scaled Ones.
The 3.0 "Savage Species" manual has some more useful-but-nonspecific features which lizardfolk can take advantage of via their more generic racial features like natural attacks. It is 3.0, so some of its mechanics will need massaging in order to fit a 3.5 campaign.