The best mage in the game is probably Edwin. He´s an evil conjurer and you can find him in Nashkell. You can get him and do his quest, that way you will get another mage (Dynaheir, good aligned invoker (i think)). Now, depending on your alignment, choose one or the other.
In Nashkell mines there is another good aligned mage, but he´s so poor and annoying, i think you really shouldnt take him.
About memorising spells, take potions to increase your intelligence and im sure you will memorise them.
------------------
"Let my spells do the dirty work" Ertai, High Sorceror of the Holy Flame