Purl Bee has a simple tutorial to make felt coasters that look like citrus fruits. Each coaster only needs two colours of felt and some matching embroidery thread.
I made a lemon and an orange as I already had some felt in the right colours, I think a lime would go well with them too. Each coaster took me about an hour and they were fun to make. They would look good as brooches if you made much smaller ones.