Seven eights is the stock diameter and it is much simpler to keep that size.
I got the protaper SE raptor bend bars (SE stands for seven eights in that brand) and I like them a lot. Higher, wider but less pull back.
Aluminum bars are more expensive but they provide more vibration dampening because they are thicker. You can't use the stock bar ends on aluminum bars but you don't really need them.
Do a search on here for handlebars. There is a thread that compares lots of different models with dimensions for each.
2006 Wee: Farkling in progress