Are we counting Vertigo? If so--
Hellblazer. Hellblazer all the way--there's nothing quite like anarchopunk blue collar magician getting his ass kicked left and right by beings more powerful than him but still turning out sort of okay because he's a right cunning bastard.
I believe Hellblazer is in fact currently running, but I think the guy currently writing sucks (Diggle), so I'm pouty and not picking it up. I'd HIGHLY reccomend the entire Azzarello run. It's low power, but kooky, and really eff'ed up. I think a lot of fanboys disagree with me, but I think it's very essentially Constantine. The Carey stuff is really good, too, but usually happens on a bigger scale.
Lucifier isn't current--however, it is awesome. However, it's about... Lucifer. So if you want a low power protagonist, it is so not what you're looking for... but it doesn't FEEL like a cape, because it isn't.