Item's that could be added to aid Attack Damage Casters in Season 3.

Reikan's Axe - Cost : 3615
+575 Health
+65 Attack Damage
UNIQUE Passive : Spell Vamp 20%
UNIQUE Passive : Your spells apply a 25% slow effect that decays over 4 seconds.

Argon's Ancient Blade - Cost : 3840
+115 Attack Damage
+35 Armor
Passive : Your auto attacks are reduced in damage by 20%.

Zephyr's Horn - Cost : 2150
+35 Attack Damage
UNIQUE Active : The damage of all physical spells are increased by 20% for 6 seconds. Cooldown 90 seconds.

This is hard to judge if you don't include what builds into them.

Reikan's
Gives too much health to also have spell vamp. One form of sustain or another, not both seems to be riots way.

Argon's
The passive is negative. There have yet to be any items or abilities that have a negative side effect (other than when they are used poorly). It's interesting but for most casters I would never buy it as I rely on auto attacks as much as my spells (Riven is a huge example)

Zephyr's
Gives far too much of a boost for so little. Riven would dominate hard with this item. What's that? Cast my ult my shield and suddenly I'm at a 44% increased damage? Even on someone like pantheon, assuming passive works likes graves' in terms of sustaining it, he could just harass with spears while pushing the lane and never lose the passive.