Multi-use ranged touch/ray spell?

[Prime32]

Are there any ranged touch (including ray) spells with a duration of 1 round or more, allowing you to attack with them as many times as you want while the effect lasts?

Stuff like scorching ray, which gives a fixed number of attacks, doesn't count. I'm looking a for a ranged equivalent to flame blade or hammer.

[Captnq]

Cloud of knives?

[phaedrusxy]

Produce Flame does have a limit, but it is high enough for most that it will last for more than one round if your CL is decent.

[Demelain]

Darkfire from the Spell Compendium. It's cleric 3, lasts rounds/level, is persistable, and you may (I'm not sure) be able to make iteratives with it.

[Nunkuruji]

Darkbolt perhaps

[Kethrian]

Definitely Darkfire.  You can't attack with it in the same round that you cast the spell, but afterwards, you can make attacks, melee or ranged to 120', as touch attacks, and make AoOs with it as well.  Note that the spell does not force those attacks to take a standard action, so you can make iteratives.

Too bad there's no special rules to give bonuses for the fact that the spell is invisible to all but darkvision ... Invisible "weapon" attacks should get some kind of bonus ...