Lemon Balm, Melissa officinalis
A wonderfully easy herb to grow (sometimes too easy, it can spread!) but essential to have in the garden. The bees love the flowers and the mosquitoes hate the scent of the crushed leaves. It is a perennial plant that can die down in winter or certainly growth slows down but will come up bells ringing in Spring.
Anti-microbial action of lemon balm makes it a great remedy for cold sores, go here to my post about making a cold sore balm using Melissa officinalis.