Having read, downloaded, or even played most of the clones being discussed here, and being bored at work today, I figured I would briefly give my thoughts on each (all of the following are IMnsHO, YMMV, etc.):
Castles & Crusades: Love, love, love it. But yeah, all of Irda's criticisms are totally valid. It's basically a cleaned up AD&D with some of bits I like from 3rd ed. thrown in. (I guess Davis and I like much of the save stuff.) Owning AD&D and 3rd ed., I could have easily done this myself, but I am very happy to have it in nice, thinnish, hard-bound book. I enjoy their monster book (particularly their stand-ins for traditional, yet non-SRD monsters), but it's totally not needed if you have any older edition monster books lying around.
Labyrinth Lord: This one strikes me as being closest to Basic/Expert D&D, with its separate, level-capped classes for demi-humans and d8-for-fighter-based HD system. Seems designed to scale up to 14th level. Haven't played it, seems solid-enough, only minor differences from its source material.
Basic Fantasy RPG: Still based off Basic/Expert, but with more stuff from other editions. Class and race are separate, and classes scale up to 20th level. Seems to have more campaign-related info than Labyrinth Lord.
All three systems use the Basic/Expert ability score modifiers (upto +/- 3, 9-12 is no bonus). The latter two use traditional effect-based saves (e.g. poison, breath weapon, spells, etc.) while C&C uses its own ability-based system. (Kind of like if 3rd ed. had 6 categories instead of 3).
Swords & Wizardry: just now heard of it. Lets see if I can get their from work.