Really, in WoW there is no "best" race for any given class. There are some attributes that weigh in the decision, but there is nothing that is crucial to the playability of a mage.
Generally, for Horde Undead get a lot of mages, mostly b/c they have the best PvP racial talent. As far as Alliance goes, not entirely sure, Humans get some nice xp bonus, Gnomes get some Int bonus, but Draneai (spelling) have lower spell hit cap and a healing spell, so personally I'd do Dran...the last one.
Toggle caps!!
Edited, May 8th 2008 4:42pm by Mhog