The Amazon Kindle Fire HD is in my opinion a well specced tablet. ( 7 inch screen, Dual-core 1.2GHz TI OMAP4 4460 CPU, 1GHz). It's a fully fledged tablet device using a customised version Android OS, rather than just an e-book reader like the original kindles.
Drawback with kindles are they can only access apps on the Amazon app store which there is about 60,000 apps, compared to approx 600,000 on the Google playstore.
As an alternative I would suggest looking at the Google Nexus 7, the 8GB version can be got for £159.