Citrussy and herby, lemongrass makes an appearance in just about every Thai recipe going, including Thai curry paste. It looks a bit like a spring onion but is much firmer, and will taste all the better for a good bruising (give it a bash with a rolling pin). If the supermarket has run out you could use lemon peel or buy lemongrass semi-dried in a jar, although these are only marginally better than toenail clippings.
Recipes with lemongrass
Chilli jam with lemongrass and ginger
Steamed mussels in a lemongrass and coconut broth