I have to admit I've gravitated toward B/X clones mostly, the best example being Adventurer, Conqueror, King system. With the Players Compendium you have a way to build infinite classes if the ones in the main rulebook don't cover the load enough. And they get pretty detailed, as well as having a bunch of premade ones just to expand what covered.
(I call 'em out on the No Halflings things, but even that's corrected in the Heroes Handbook, or you could just make up your version of hobbit from the PC easily enough.)
The whole game shows how you can pull B/X apart by the bolts and the core structure underneath is really mechanically sound. Alexander Macris shows how the whole thing works and makes something of real beauty if it's close to what you're looking for.
For other games, I've been attracted to Swords & Wizardry with its One Baleful Saving Throw for a while now, and may try to throw it into the rotation sometime. I also like some of Lamentation of the Flame Princess with its skill class and inventory, as well as the Summon-Of-Doom as a first level wizard spell. If I ever run Carcosa it'll probably be with that.