I am surprised no one has mentioned Castles and Crusades yet, since that is meant to be a simpler version of OGL D&D. Another "option" for 3.5 would be to use only the three generic classes form Unearthed Arcana (warrior, expert, spellcaster) also in the SRD.
I can see options getting overwhelming if people feel that a game requires them to take the strongest options. Less so if they do not. If I am happy playing a Human Samurai (yes I deliberately picked a Tier 6 class) in 3.5, then I don't have to worry too much about options, particularly if I make my feats the once that only have to get factored in once, like Iron Will. Similarly, I could play a Warlock in 4.0 that only uses fey based powers, and fey based paragon and epic lifestyle choices, and rock the house with it, but I bet it is not anything near to optimal. Mind you, that already covers at least 2 player books in 4.0, but that is a slightly separate issue.
Similarly, some complexities go away by ignoring them (assuming the DM lets you). So the weapon vs. armor tables of 1st ed. AD&D, encumbrance rules in, well, every single iteration of D&D and D&D-like games, etc., can just drop out.
That said, there is a reason I like point-based games like GURPS and M&M more if there are templates available to just take (a reason I like Warriors and Warlocks and likely will like the DC Superheroes stuff for M&M - "I wanna be like the Flash? Well here he is!"). It takes away the "did I leave the oven on?" problem of failing to consider a character creation option that was kind of important to take.
And of course some options seem to come dripping with flavour. The Warlock in 3.5 was one of those. It also was a good option IMHO because it simplified things considerably. I would make it the go to character for a new player wanting to be a magic using type, as well as for a DM that needs a fast villain. It has practically no paperwork!
Another option is to try replacements rather than additions. Like (these are all 3.5 examples) take out arcane magic but allow psionic powers. Or only allow the PHB II 4 base classes and Races of the Dragon races and see where that goes. Or go heavy on a book like Sandstorm. I guess in 4.0 one could try something like "only primal as a power source" and see what happens.