Just wanted to put a word in for 2 [out of the way] grocery stores which we find ourselves buying from regularly.
First, there is Kingsbury Fruit and Veg on Kingsbury Road (if using public transport, right out of the tube station about 50 yards up on the same side of the road) which in addition to the obvious sells a wide range of Indian groceries all at good prices. The bulk of our 2007 Alphonso mango purchases came from this store and they were very tasty and well priced. Nearby there is a Gujurati sweet/savoury shop called Gayatri (www.gayatri.co.uk) which my mum likes a lot and a recent sampling of their samosas impressed.
Secondly, when visiting close family friends in Kingston, we always stop at a large Iranian/Middle Eastern grocery store called Suroor, 101 Robin Hood Way. Really nice people and a very good selection of meats, fruit+veg, deli items and general groceries from all over the Middle East, Iran and the Gulf. We adore their skewered chicken kebabs especially when eaten with barbari nan, salads and relishes etc. But there are lots of other good items besides, definitely worth checking out if you find yourself in the area.