I started on Betonmarkets which is mainly Fixed Odds and then progressed to their sister site Xodds because they also offer a spread betting facility but only on Foreign Exchange. However the beauty of this is you can trade 24hrs per day during the week.
They open a virtual account for you with a balance of 10000 USD or £ to start. I've been using it since Feb and I haven't lost much money yet, which I suppose is a good sign. Mind you I haven't won much either! Tend to hover just above or below the ten grand mark. I'm still learning though!