Tamarind dipping sauce
1/2 tub Tamarind paste
salt and chilli (green or dried) to taste
Hunt down Blue Dragon tanmarind paste if you can, it's MUCH better than Barts, you'll probably find other makes in Asian shops but BDs the best I've tried.
Put all the ingredients in a blender and whizz till smooth, some people like it thin others quite gloopy, likewise with the balance of hot/sweet/sour, fiddle with it till you're happy with consistemcy and flavour.