Here's the one I do often and you can see a photo of it in the gallery
plain natural yoghurt (or greek yoghurt as per Rebecca's recipe)
cucumber, cut in half, watery centre removed, grated
mint, either dried, or mint sauce (like you use in lamb)
mix the cucumber into the yoghurt to your liking
add the mint to taste, not too much as you don't want to over power the yoghurt/cucumber taste
a very little salt to taste