Is there any reason a Duskblade
cannot cast rays or other ranged touch attack spells via their arcane channeling? The actual ability in question says;
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. . . you can use a standard action to cast any touch spell you known . . .
The thing is, it doesn't specify if it means a spell with
Touch Range, a spell that makes a
Touch Attack or both. All ray spells are considered touch attacks, and much like Touch range spells require an attack roll vs the target's Touch AC and can crit on a 20 (or 19-20 with the Imp Crit Feat). The only difference is touch range spells are a
melee touch attack and rays are a
ranged touch attack.
Suppose there are a few weird cases like Chill Touch where they just say make a touch attack and aren't called out for being touch attacks, though I think that is because they buff your hand and you can discharge the attack as a separate action. I suppose if we wanted to be really petty about RAW if you say a Duskblade can channel Chill Touch they can't channel Touch of Idiocy, and vice versa.