TidBITS publishes a line of inexpensive and very useful PDF E-books, mostly dealing with Mac OS X subjects. I have read and reviewed a number of these and highly recommend them to you.

Take a minute to browse through their titles:

• Take Control of Bookle
• Take Control of Screen Sharing in Lion
• Take Control of iTunes 10: The FAQ
• Take Control of Mail on the iPad, iPhone, and iPod touch, Third Edition
• Take Control of your iPad
• Take Control of iCloud
• Take Control of Backing Up Your Mac
• Take Control of Spotlight
• Take Control of Using Lion
• Take Control of Upgrading to Lion
• Take Control of TextExpander
• Take Control of Troubleshooting Your Mac, Second Edition
• Take Control of Speeding Up Your Mac
• Take Control of iPhone and iPod touch Networking & Security, iOS 4 Edition
• Take Control of iPhone Basics, iOS 4 Edition
• Take Control of PDFPen-5
• Take Control of Mail on the iPhone and iPod touch, iOS 4 Edition
• Take Control of iTunes 10: The FAQ
• Take Control of iPad Basics (FREE!)
• Take Control of Media on Your iPad
• Take Control of Working with Your iPad
• Take Control of iPad Networking & Security
• Apple Mail in Leopard
• Apple Mail in Panther (Leopard version also available)
• Apple Mail in Snow Leopard
• Apple Mail in Tiger (Leopard version also available)
• Back to My Mac
• Booking a Cheap Airline Ticket
• Buying a Digital Camera
• Buying a Mac
• Customizing Leopard
• Customizing Microsoft Office
• Customizing Panther (Leopard version also available)
• Customizing Tiger (Leopard version also available)
• Take Control of Digital TV
• Easy Mac Backups
• Exploring & Customizing Snow Leopard
• Font Problems in Leopard
• Font Problems in Mac OS X, Tiger Edition (Leopard version also available)
• Fonts in Leopard
• Fonts in Snow Leopard
• Fonts in Mac OS X, Tiger Edition (Leopard version also available)
• Getting Started with DEVONthink 2
• Getting Started with Dreamweaver
• iKey 2
• iPhone OS 3
• iWeb '06
• iWeb '08
• iWeb '09
• Mac OS X Backups, Fourth Edition
• Mac OS X Lexicon
• Mail on the iPad, iPhone, and iPod touch
• Maintaining Your Mac
• Making Music with GarageBand '06
• Making Music with GarageBand '08
• Making Music with GarageBand '09
• MobileMe
• Now Up-to-Date & Contact
• Passwords in Mac OS X
• Permissions in Leopard
• Permissions in Snow Leopard
• Permissions in Tiger (Leopard version also available)
• Podcasting on the Mac
• Recording with GarageBand '06
• Recording with GarageBand '08
• Recording with GarageBand '09
• Running Windows on a Mac, Fourth Edition
• Safari 4
• Safari 5
• Screen Sharing in Snow Leopard
• Sharing Files in Leopard
• Sharing Files in Panther (Leopard version also available)
• Sharing Files in Snow Leopard
• Sharing Files in Tiger (Leopard version also available)
• Spam with Apple Mail
• Switching to the Mac
• Syncing Data in Leopard
• Syncing Data in Snow Leopard
• Syncing in Tiger (Leopard version also available)
• Thanksgiving Dinner
• the Mac Command Line with Terminal
• Troubleshooting Your Mac
• Upgrading to Leopard
• Upgrading to Panther (Leopard version also available)
• Upgrading to Snow Leopard
• Upgrading to Tiger (Leopard version also available)
• Users & Accounts in Leopard
• Users & Accounts in Panther (Leopard version also available)
• Users & Accounts in Tiger (Leopard version also available)
• Users & Accounts in Snow Leopard
• VMware Fusion 2
• VMware Fusion 3
• What's New in Entourage 2004
• What's New in Word 2004
• What's New in Word 2004: Advanced
• Your 802.11n AirPort Network
• Your AirPort Network
• Your Domain Names
• Your iPhone Apps
• Your iPod: Beyond the Music
• Your Wi-Fi Security
• iPhoto '08: Visual QuickStart Guide
• iPhoto '09: Visual QuickStart Guide
• iPhoto 6: Visual QuickStart Guide