It was in the slow cooker for a good eight or nine hours yesterday so it was already rather delicious (if I do say so myself). but you're right about it improving.Nice, love curry the day after it was made. The flavours all seem to have mingled together better.
I normally like spicy curries, but I'd made a thicker and more sweet and sour style (not the Chinese rubbish) one my mate recommended - being an Indian himself.
He actually recommends making a curry and leaving it in your car boot for a day or two to, as he puts it, 'mature'. Apparently, the coldness of the fridge ruins it.