After the issue of a lack of decimal places on current exchanges came up with Ducknote, I set out to write an exchange which supports 3 decimal places past a satoshi. The base unit for prices on the exchange was a satoshi to make things simple. That exchange has since been updated with a new website, and many new features. I have also recently added Dashcoin to the exchange, as I saw its need for prices below a satoshi.
The updated exchange has been under a closed beta, and I will be opening it to the public tomorrow.
Which exchange?
It is a new exchange based on my old ducknote exchange. You can see its thread here https://bitcointalksearch.org/topic/subtoshi-new-exchange-allowing-11-decimals-764158