Speaking from the black mage repertoire (besides the obvious biggies like Despair, Paradox, METEOR, etc)... it would probably be Aetherial Manipulation. The funny thing about Ves is once she gets a feel for someone's aether signature (friend OR enemy), she can zip right to them. No one ever expects the black mage to get up close and personal, and Ves loves catching her opponent off guard. Also, for someone close to Ves like Y'shtola, since her aether is so ingrained to being around her, Ves can zip to her from some pretty far distances, along with some other neat things (untested, very dangerous but could be useful if the situation was dire!)

Outside of the regular black mage fare... honestly one of her favorite spells to cast is one she came up with called (for lack of a better term) leyline land mines. Basically she can create areas where certain spell effects will trigger if something of enough aether density enters them. Ves rarely get's to do anything sneaky like that post-WoL, but casting a spell she came up with, using actual preplanning and incantations? Extremely fun for her!