The attached video will show an easy, zero-risk method for utilizing poor pathfinding AI to easily dispatch all three giant club-weilding Barbarians near the Valley of Drakes / Londo Ruins entrance to Blighttown.
All you need to do is get their attention, then run back to the ladder that goes down into Blighttown and climb down a rung or two. The Barbarians will chase you, then fall to their deaths when they get to the wooden walkway. I was never able to get more than one of them to follow me at a time, so if you want to kill all three of them using this method, you'll probably have to run back and get each one to follow you one at a time. But at the very least, you can get rid of one or two of them and make fighting the last one much easier.
They are big and slow, so it's very easy to run away from them, and if you're coming into Blighttown from the Londo Ruins / Valley of Drakes entrance, then it's also pretty easy to just run past all three without taking any damage. The only thing you might have to worry about is having one or two of those annoying mosquitoes sneak up on you. So watch out for them. Assuming that you are actually able to hit the mosquitoes, they are one-hit-kills, so they shouldn't give you too many problems.
The loot that the Barbarians drop can be picked up by continuing down the ladders and looking on the second level above where you get onto the giant wheel elevator. You'll have to fight a few of the giant tick things, and if you haven't cleared the area already, be weary of enemies firing toxic blowdarts. The Spider Shield is a must-have for this area.
This trick takes advantage of poor pathfinding AI. Demon's Souls had some pretty bad pathfinding too. What's ironic though, is that according to the Dark Souls wiki, the AI pathfinding code causes severe framerate slowdown in this area. So the pathfinding AI decreases the performance of the game, but it doesn't increase the performance of the enemies. It's a win-win! [sarcasm intended]