I'm not sure if there are any mods to enable leaning, but I thought I'd add that. Something that I've felt has been lacking from Half Life ever since it has become a bigger part in games, is iron sights. I just think it would feel better to aim down the sight with the guns in Half Life 2 now, so I was wondering if anyone has tried any out and if you could recommend me one. I haven't searched for a leaning mod, but that would be pretty cool too in my opinion. Thanks.

Eww. Leaning I can get behind, but iron sights are pointless when the center of the camera is always the target.

Iron sights and leaning would pretty much break the game, but there's this crazy mod I love called SMOD Redux that does it. It adds those 2 features among a bajillion other dumb things, like UMD launcher PSP, bullet time, Dark Messiah style physics-enabled kick, and explosives littered in cutscenes that would break the game progression if you don't catch them before the NPC's bump into them. I honestly don't remember how to install it, but here's the website.

@audiobusting: @ezekiel: I still think the enemies, from an animation perspective go down in satisfying ways when you shoot them, but not being able to aim down the sights to me feels too archaic now when playing Half Life, when it's an otherwise fantastic experience still. Leaning would be a nice plus to me. Yeah, I saw that mod, but it looked like it changed too much. I don't want to really change a lot of its identity, I just want to implement a nice iron sight function, and leaning if possible.