Moo, there's nothing I like better than a generous man.
Although you've already covered jewelry, there's never any harm in getting her more. After all, diamonds are a girl's best friend.
How about a modest diamond tennis bracelet? There is one to fit every budget, although I don't really think you even have a budget.
Some classic diamond studs, perhaps? Mounted in a metal that matches that of her necklace.
Perhaps you could buy her a lovely gold or white-gold, or heck, platinum, charm bracelet? Of course, just add a couple of charms to get her started, but let her fill up the rest of the spots. You could give her charms for other occassions, also!
My boyfriend is really big on the jewelry, because frankly, he can't think of anything else to get me, and let me tell you: I NEVER MIND! I think she'd love jewelry.
XOXO,
Annie.