At will negative levels

[Renen]

So, what ways does everyone know that can give you an at will attack that bestows negative levels?

Templates, races etc. Are a go!

[Mando Knight]

Vampires cause 2 negative levels with their slam attack. Wights also cause negative levels, but don't have a LA (and thus aren't playable).

There's probably more, but those were the ones from off the top of my head.

[Rebel7284]

Wasn't there a soul eater PrC that gave that?

Edit, yes, yes there is, in book of vile darkness. I recall it's nice in some grappling builds. =)

[Darrin]

In Defenders of the Faith, there was an Energy Drain property that you could put on a shield that could give you an enervation effect whenever you shield bashed.

It was reprinted in Ghostwalk, but the designers eventually noticed it was overpowered and added "This attack may be used once per day." in the Ghostwalk 3.5 update.

However, if your DM doesn't allow Ghostwalk in his campaign...

[Callin]

Necropolitan wielding a Life Drinker from the DMG