Check out "The Missing Manual: Lion" by David Pogue. Chock-full of info and easy to read. I've been a Mac user since 1995 and I always keep a copy handy. The Kindle edition is less than $10.
Essential apps:
1Password for managing passwords, credit cards, software serial numbers... you name it. Web surfing and online purchases are one-click experiences. Secure encryption protects your data. Also works with iOS devices.
Jumpcut is a Clipboard replacement that puts an icon in the Finder Menu Bar. It retains items in the Clipboard instead of replacing the previous clipping. You can decide how many clippings it will save and delete them when you choose to do so. Very Handy!
Cookie makes managing cookies across multiple Web browsers a snap. Designate favorites so you don't have to repeatedly login at your fave websites. Easily delete tracking and other cookies.
ABMenu for accessing your Address Book from the Finder Menu Bar.
DropBox for syncing files across multiple Macs and access to files from iOS devices.
Vienna, a free RSS reader that places an icon in the Finder Menu Bar. It beats any RSS reader that I have tried; I gave up on NetNewsWire when I discovered Vienna.
Witopia's personalVPN to secure online data transfers when traveling and at home. Secure encryption and your IP address is hidden as a bonus. YOur ISP is prevented from tracking your online activity. Also works with iOS and Android devices, as well as Windows. You can use one account on multiple devices for less than $6/month.
Bookmacster for managing bookmarks across multiple Web browsers via the Finder Menu Bar. Sync bookmarks via DropBox or iCloud.
Fantastical for easy access to your calendar items via the Finder Menu Bar. Add events by simply typing the details into Fantastical. It automatically places the info in the proper fields.
DEVONthink, a database on steroids. Similar to Evernote, DEVONthink is much more powerful due to its Artificial Intelligence. If you do research or simply have a lot of files on your Mac it beats Finder file-management hands-down. I do medical research and I could not effectively get the most out of all my data without DEVONthink. It handles and displays just about any file-type out there without having to open other apps, getting data into DT is easily accomplished in a variety of ways and its search function provides results in ways that blows Spotlight out of the water.
Airfoil for streaming any audio (not just iTunes) to other Macs, iOS devices and home audio systems connected to an Airport Express. I use it with Pandora and Spotify.
TimeOut for scheduling automatic reminders to take a break to stretch and give your back/neck/arms a rest.
CheckOff, a To Do list accessible via the Finder Menu Bar.
Most of the above apps are available as free demos, so you can try before you buy. And a few are free to begin with!