2nd level spells is where Illusion really shines. Two of the most useful and powerful low level Wizard spells, Invisibility and Mirror Image, are both 2nd level Illusions. Blur and Minor Image are also very useful.
And don't forget the new "must have" combat spell, Scorching Ray. False Life is also a no-brainer. If you have a spell slot to spare and don't know where to spend it, get False Life. More HP never hurt.