Buy spices from an ethnic grocer rather than a supermarket: prices are surprisingly low and quality is top-notch. Good brands of spices will have a strong aroma and the packets will be free of dust and other debris. The aroma and colour of ready-ground spices can quickly fade; many experts insist that the best flavour comes from toasting and grinding whole spices yourself just prior to cooking.
Some of the authentic ingredients of South East Asian cuisine, such as galangal (a member of the ginger family) or Thai red and green curry pastes, may need to be tracked down at specialist retailers, but other typical ingredients such as fresh chillies, lemongrass, garlic and ginger are readily available in supermarkets. In South East Asia, many households rely on convenient ready-made curry pastes purchased at the local market, so you should not hesitate to use them, especially authentic brands from specialist stores.