Duskblades have the ability Arcane Channelling, which allows them to cast touch spells through a melee attack with their weapon. Can they only channel Duskblade spells this way, or can they channel any touch spell they can cast (specifically, inflict wounds from multi-classing to cleric)? Or is there something in between?
Yes. And they kick a lot more butt doing so, as opposed to those low-key Duskblade spells.
Duskblades can channel "any touch spell [they] know," beginning at third level (PHB2, p.20 - thank you @BESW). I've pulled this off before and it rocked. Contagion, bestow curse, inflict and cure spells (the latter for undead) work decently in varying degrees, at least for starters.