Ranged Touch Attacks Can Inflict Sneak Attack Damage
Although it's implied by the Player's Handbook, Complete Arcane clarifies this in the section Weaponlike Spells
Any spell that requires an attack roll and deals damage functions as a weapon in certain respects, whether the spell deals normal hit point damage, nonlethal damage, ability damage, or energy drain. Such spells can threaten critical hits, can be used in sneak attacks, and can be used with favored enemy damage bonuses. You can even use a number of combat-enhancing feats from the Player’s Handbook to improve the effectiveness of weaponlike spells... (85)
A spell that requires a ranged touch attack require an attack roll. If the spell also deals damage, it can inflict sneak attack damage if sneak attack's conditions are met.
A successful sneak attack with a weaponlike spell deals extra damage of the same type as the spell normally deals.... The exception is spells that deal energy drain or ability damage, which deal negative energy damage on a sneak attack, not extra negative levels or ability damage. (CAr 86)
Thus, for example, the Rog1/Wiz3 who casts the 2nd-level Sor/Wiz spell scorching ray [evoc] (PH 274) can inflict with that spell an extra 1d6 points of fire damage by meeting the requirements for inflicting sneak attack damage, and, for example, a Rog3/Wiz7 who casts the 4th-level Sor/Wiz spell enervation [necro] (PH 226) can inflict with that spell an extra 2d6 points of negative energy damage by meeting the requirements for inflicting sneak attack damage.