Just completed my first trade on the Coinffeine decentralised Bitcoin exchange! It's very slick. A great example of a decentralised, p2p Bitcoin app.
And best of all it's built with bitcoinj, JavaFX and Scala, tech I've been pushing for a while now. You wouldn't know it to look at it though.
) decentralises the Bitcoin side of trading, whilst giving you a traditional (but open source and fully client side) order book style interface. The fiat is transferred using OKPay and the whole thing happens in chunks, so lowering the trust required. It's not as fully decentralised as BitSquare is, but it avoids the need to manually set up wire transfers and the like.