The only one I've played is faiakes mod v2.4. I like it. Some people don't, as it is really just a very large compilation of mods. Some people only want a few crucial mods, keeping the base STALKER mostly there. And the number of mods in faiakes is kind of ridiculous but a lot of them I like. I went on a STALER mod hunt a few months ago. I haven't played any yet but here's what I downloaded:
Twilight K.E.T - looks great from what I've read in the readme. But note that it seems like faiakes in that it has a ton of modifications so it may not be for someone who wants to mostly preserve the original game.
Priboi Story - Another large modification but from what I've read and as the name implies, it's focus is a much different main story and not so much a large collection of small mods. Probably best for someone who has completed STALKER already.
OLmod by Bolm - without posting the change list, it does make quite a few changes, but comes in at like 1/5 the size of the above mods so I'm not sure what the deal is
There is also Oblivion Lost, ABC/ABC Inferno, AMK, SRP, and this one that combines like three large mods.
All in all it is kind of hard to figure out what is what and good. But reading these changelogs for the mods I listed, man makes me want to fire one of them up right now! So mainly I just wanted to post some names on some of the more popular large mods I found. I actually would like to see some comments from people who've played several mods to sort of rank them or give the gist of what they are/do.
Zenoth: What ever happened to that new ABC Inferno? I never played the old one as I was going to wait for the new big release, but I don't think it ever happened?
Meh, all that work searching for mods, when AMK looks like what I should go with. I think I passed it over before since I thought it was Russian only or something.