Is there a piece of jewelry you don''t have that you really want? That is what I would ask him for. Probably earrings or a nice necklace that you can wear that day! But then again I dont'' have a whole lot of stuff so for me anything sparkly!
A necklace doesn''t have to be expensive though. Do you have something you like or maybe an amount he wishes to stay under. Even something plain but sentimental would be nice. A heart pendant or a small gemstone. What do you like.
For a occasion I would look for something casual you can wear when you want. Something more sentimental then anything and I did find this which I really like and it is inexpensive.