So you wanna cook Indian...

First thing you will need is a large quantity of spices.

Head to an Indian grocery, they have big bags of spice, for less money than the little containers at the normal grocery store.

Some spices you should have:

cumin, ground

cumin seeds

coriander, ground.  

coriander seeds, but we have not needed them frequently

paprika

turmeric

red chili powder

ground cardamom (we dont use this one much either)

cardamom pods

cloves

cinnamon stick

black mustard seeds

garam masala

amchoor

hing (asefoetida) 

A special note regarding hing (also known as asefoetida, devils dung, or stinking gum!)

Keep it in an airtight container or else it will infiltrate all your spices, we keep it in a tupperware container.  It has an extremely pungent aroma when uncooked,  to me it smells like burning metal cutting oil--  BUT when heated it has a garlic/onion aroma which is very pleasant!  If you put a little sprinkle into some heated ghee or oil it instantly changes to a very pleasant aroma.

Another 2 important staples we use a lot of is ginger paste and green chili paste.

Oh yeah, and Basmati rice!  Yummmm, we like Tilda brand, but have used others in the past.

Ghee is also nice to have, but you can substitute vegetable or olive oil to keep a lot of the vegetarian dishes vegan.