SQL Books

Simply SQL by Rudy Limeback
Introduction to learning SQL

SQL Cookbook by Anthony Molinaro
Each recipe demonstrates how to accomplish a given task. Perfect for quick example code to 'make it do the right thing''.

Oracle SQL Pocket guide by J Gennick
Bargain priced SQL reference for Oracle Database 10g, R2 including the free 10g Express Edition (XE), Microsoft SQL Server 2005, MySQL 5, IBM DB2 8.2, PostreSQL 8.1 database.

PL/SQL Books

Oracle Built in Packages by Steven Feuerstein et al
Syntax Reference book for Oracle's built-in packages, with extensive examples.
The sample code can be downloaded from oreilly.com

Oracle PL/SQL Programming by Steven Feuerstein et al.
The definitive PL/SQL book
(5th Edition Oct 2009)

Oracle SQL*Loader by Jonathan Gennick
Load data into Oracle with SQL*Loader.

Also see: Oracle DBA Books