KS4 PSHE Study Guide by CGP Books
This book is full of clear explanations of the key issues that come up in KS4 PSHE lessons. The whole thing's designed to make studying PSHE straightforward - difficult issues are dealt with in an approachable way and at the end of every section there's a page of questions to check how much you've taken in. It's all explained in straightforward language with the odd joke thrown in to help break up the work!