Any good Indian cook will have a 'dabba' (tin) of spices essential for making pretty much any curry from their region. My Mum gave me this tin when I moved out of home to go to university - unfortunately I wasn't a very good cook then (to put it kindly) so it didn't get used until years later when I got interested in cooking.
These are the spices that are used most often, there are also some others which you'll find in other tins - things like a few cloves, asafodeita, dried chillies, ground cumin instead of cumin seed. Black mustard seeds are one of my favourite ingredients and I use it in things other than Indian cooking, they are quite different to yellow mustard seeds, if your supermarket doesn't have them try your local Asian grocer or health food shop.
If you want to buy your own tin you can also find them in Asian grocers or have a snoop on ebay, there are lots on there! Once you've got all your spices, remember to replenish them every few months otherwise they tend to go stale and lose their punch.