Introductory Philosophy
There are many introductory philosophy books aimed at first-year students meeting the subject for the first time. Here are a couple of books we've used that contain handy summaries or suggestive links between different philosophers.

Philosophy: A Very Short Introduction (Very Short Introductions)The Problems of Philosophy (OPUS)A Rulebook for Arguments
Philosophy: A Very Short Introduction (Very...
by Edward Craig
£4.76
The Problems of Philosophy (OPUS)
by Bertrand Russell
£5.49
A Rulebook for Arguments
by Anthony Weston
Descartes to Derrida: An Introduction to European PhilosophyThe Pig That Wants to Be Eaten: 100 Experiments for the Armchair Philosopher
Descartes to Derrida: An Introduction to Eu...
by Peter Sedgwick

A bit more traditionally philosophical -- useful for students.
The Pig That Wants to Be Eaten: 100 Experim...
by Julian Baggini

Suitable for children, very light, a bit repetitive but fun for complete beginners.