"Spell It Out"...

[prism]

... by David Crystal.

I got this for Christmas, and it's brilliant. I recommend it to pedants everywhere.

What's so good about it? (I have a birthday coming up and have enough candles & chocs)

It's very comprehensive, and although it's pretty technical about the origins of words and their spelling, it's entertaining. Enables you to back up your pedantry with an amazing depth of historical fact. There's an odd omission in that he doesn't cover the subject of words imported from languages that have a completely different alphabet or no phonetic alphabet at all, and the effect that has on spelling in English, but apart from that, every spelling base is covered.

Sounds interesting!