What kinds of Indian foods do you like? Any particular region you prefer the food from? Hopefully, as noted above, you have an Indian market nearby, though of course, anything can be bought online these days. The lists given by
thymeless above, are pretty good, and if you have the Indian market nearby, you should be able to get the fresh curry leaves.
Back when I started making Indian food,
I really didn't like almost everything I had, up to that point, because so much of it had cinnamon in it - raw cinnamon. And almost all store bought garam masala had raw spices in it, but when I made some from a recipe in which all of the spices were dry roasted in a skillet, and the flavor was totally different! So I started getting into Indian cooking, and
finding more and more spices I needed. And I found recipes for spice mixes, and almost all had toasted spices, which made them delicious.
One of the essential ingredients you will need, and most supermarkets won't have, unless maybe in an Indian neighborhood, is the coriander seed they use - a sort of gold one, and oval, instead of round, brown variety, from other areas. No other spices I've seen with different varieties like that, except black pepper, which is more a regional thing, and the dried chilis. The small ones, like the Thai and small Chinese dried peppers are used a lot, but also in a larger, milder Kashmiri peppers, which is what is usually used when they refer to simply "chili powder", not our Tex-Mex mix of chili powder. Many others, too, but these are the usual ones. You can also use some Numex, in place of the milder ones, or chile de árbol, or similar peppers, for the hot ones.
Here is a photo of the box of the "most used" spices, along with the curry leaves.
Indian spices by
pepperhead212, on Flickr
Curry tree 9-5 by
pepperhead212, on Flickr