Ideal capsule wardrobe (for office job type):
1 or 2 pairs smart black trousers
1 or 2 smart trousers in any other colour
1 or 2 smart skirts, probably 1 black/navy
1 good winter coat
1 good summer jacket / suit jacket
a selection of t-shirts, tops, knits, shirts, blouses etc that go with at least 2 of the trouser/skirt options
(n.b. how many tops etc you choose will determine if you have 6 outfits or 600 - I'd say more than 10 and it's not a capsule wardrobe!)
1 or 2 cover up/cardigan type things for cooler days.
I think the whole point of having a capsule wardrobe is that you can put on your trousers/skirt and know that whatever top you pull out will match. So you're not stood around in the morning in your knickers screaming that you've got nothing to wear!
For those who say accessories are the key, I think that depends on you personally, I don't wear a lot of costume jewellery, I wear the same things every day. I do have 6 or 7 handbags which I change according to mood or outfit, but other than that I stick to the same 'style' and the same looks but on a rotated basis, so I'm not wearing the same trousers or colours from one day to the next.
Most women I know have their own version of a work 'uniform' - whether it takes them a week, 2 weeks or even a month to rotate through it!