I started making my own curries after buying a recipe book for Thai food last summer in Australia. I started with a basic green curry recipe and have been modifying and improving from there. It always has a bit of a flat taste, like something was missing.
My first discovery was to stop watering down the coconut milk. There was just no reason to do that.
The second discovery was that I just needed to add a lot more salt than I'd been using. This brought out the flavor a lot more.
The discovery I made tonight was that I squeezed half a lime into the pot. AWESOME. It tastes orders of magnitude better. Not necessarily like lime, mind you, but just...good. My original recipe called for lemongrass and I very rarely have that on hand, so I think the lime juice filled that void.
Not that I should be having curry anyway, or limes either, for that matter.