I had this same question when creating my Wizard.. the character sheets I had didn't allow a spot for a bonus cantrip.
But we allow it in our campaign. I don't know if this is the best source or not, but the character creation program on the CD-ROM that comes with the PH gives a bonus cantrip for specialists.
Well, specialists can't cast 0th level spells of their opposition school. If they suffer that penalty, I don't see why they shouldn't get a bonus 0th level spell to compensate.