Have a look at the British Society of Echocardiography image library
http://www.bsecho.org/education.
It is currently member only but membership is fairly cheap. Also have a look at a new open access journal http://www.echorespract.com/. It has a images and video section which will build up over time.
The Toronto General Hospital Department of Anesthesia and Pain Management Virtual Transesophageal Echocardiography Website offers a great standard view application
There is an echo image bank at the Association of Cardiothoracic Anaesthetists' (ACTA UK) website. It is due some significant additions in August. It is available to non-members of the society.