3) Persistent AoE debuffs and damage spells. I mean spells like web, Solid Fog, Cloudkill, Wall of Sand(debatable if you can concentrate on it), Haboob etc. These spells affect the target continuously for as long as they stay in the area. Channeling them makes impossible for the target to exit spell area, so they are affected for the full duration (sometimes minutes/level), so IMHO these are by far the best spells to channel into weapons.
This is the bit of optimizing I've managed to come up with so far. I'm looking for input (other abilities, feats, tactics, specific spells) to make Channel Spell better)
Clever boy. Channeled Cloudkill
is quite nice. So then the best optimization would be find ways to add effects/damage to the round by round effects of AoE spells. Seems like there should be plenty of ways, but I've not looked into it before.
*goes bookdiving*
Black Lore of Moil
adds pretty much free damage to spells like Acid Fog, and a good bit of it (4d6 negative per round on top of the 2d6 acid). They can't escape it, there's no save, and it doesn't use up a higher spell slot. Rats! Well, if you can find a way to make other spells Necromancy this is cool... still usable for stuff like Kelgore's Grave Mist (economy damage over time +Fatigue) and Pulse of Hate (for when you really need to deal 6d6 damage per round, lol).
Chain Spell allows you to chain the channeled AoE to other targets within 30ft, and since it's channeled AoE those targets also get no save and also cannot escape the effects. Sweet, but it still takes up a three levels higher spell slot. I like this a lot, presuming I'm interpreting it correctly.
Something I just thought of that's unrelated to AoE spells: You can transfer spells with a range of Personal to targets you hit with your weapon. So, channel a personal buff into your fist, and then punch your friend in the shoulder. Voila! You are able to transmit buffs you never could before!
Anyway, back to AoEs.
Channeled Prismatic Mist just seems like barrels of laughs.
Hrm, actually this seems to be all I can find, but I by no means have all of the best resources available for optimization.
EDIT: You can even channel spells that make no sense. In the description you gave it specifically says you can channel ANY spell available to you, and it replaces the casting time, the range/area, and the targets of these spells you channel. This allows for really weird stuff to happen. Starting from normal to most bizarre:
1) Channel Major Creation onto your foe, bypassing the normal 10 minute casting time, and dousing them in your favorite poison (they have an open wound from your attack if you prefer Injury poisons).
2) Channel True Resurrection onto an Undead for the lols.
3) Channel Goodberry onto a kitten.
4) Channel Guards and Wards onto an enemy. What. The. Fuck.