Probably the best PLSQL and SQL book

Rampant press has produced a few probably best oracle books that explains concepts intuitively:

Easy Oracle PL/SQL Programming: Get Started Fast with Working PL/SQL Code Examples (Paperback)

by John Garmany


This book is probably much better than PLSQL for dummies or the online manual. I am getting a copy from Amazon. Sample can find in google books.

Easy Oracle SQL: Get Started Fast Writing SQL Reports with SQL*Plus (Paperback)

by John Garmany

This book is probably better than head first SQL.