GRave Defense HD - Free Tower Defence Game
If you've never played a tower defence game, it's a mix of strategy and resource management where you build weapon emplacements to defend against hordes of attackers. It's very easy to get into and great fun as the weapons and attackers get more and more powerful.
One criticism would be that the waves do seem a bit on the long side, but aside from this it has smart graphics and runs beautifully on the UK Kindle Fire.
The app can be downloaded from GetJar (instructions here)
Web page: http://www.getjar.com...
Quick Download Code: 264186