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.