Lavender lemonade is amazing, as is limeade. Actually, adding lavendar to almost any fruity drink is a good idea. Make up a lavendar simple syrup, and use that as sweetener.
I had an amazing lavender creme brulee a couple years ago at a place that is no longer open.
Combining Lavender with rosemary is also a good idea for any of the above treats.
And, obviously, Lavender ice cream (Molly Moon's has a honey lavender that is really good) or sorbet is a good idea. If you're making sorbet, go with a citrus-y lavender, or even a lavender mint combo.