I have only used this for a couple of hours but it seems, initially, to be excellent. It is the Android version of the dictionary and has just been released. The publisher is Paiboon and it is available in the Google Market. It cost me just under £ 16, so about 800 baht.
I first saw a Thai "talking" dictionary when i was studying for my CELTA. Over ten years ago, it had cost over £ 80 at Pantip and wasn't much good.
This also explains the reasoning behind the sound of the words and is very helpful to me as I struggle with the tone marks.
The Paiboon site can be found here :
Learn Thai the Easy Way!
Not a cheap app but I think it is worth the money.