Having a second monitor for your desktop or laptop can greatly boost your productivity. That extra screen real estate really helps you work (and play) better. Using AirDisplay, you can easily turn your iPad into a second monitor for your PC or Mac. Also available for Mac. ($9.99)

GoodReader is, at its core, a reading app – but it can do so much more. It supports most file formats, including audio, video, and MS Office, allowing you to consume and organize your media in one place. GoodReader also syncs with remote servers like Dropbox, SkyDrive, SugarSync, and any other WebDAV, AFP, FTP, and SFTP servers. GoodReader is a must have for any iPad user. ($4.99)

If you’re the type who returns from a trade show or networking event with a fist full of business cards, it’s time to replace your rolodex with digital contacts. A digital library of contacts is much more portable and easily searchable to better find what you need. With CardMunch, snap a picture of a business card and their team will transcribe it and push its contact info back to your device. (Free)

The concept of making a list hasn’t really evolved over time, but Clear will give your lists grace and personality. Clear is a stylish, intuitive list-making app with a super sleek interface. The multitouch gestures make it easy to check items off, make new lists, insert items, etc. Also available on Mac. ($1.99)

Some people think that the built-in apps just aren’t powerful enough. Think of Checkmark as a souped up version of Apple’s built-in Reminders app. Super easy-to-use, you’ll be setting up reminders based on location and/or time in just a few taps. If you find yourself unhappy with the way Reminders performs, give Checkmark a spin. ($4.99)

Designed for note-taking and archiving, Evernote allows you to store and tag text, audio, photos, drawings, and webpages into easily sortable entries. Write a note on a piece of paper, snap a pic with your phone. From there you can tag, annotate, leave comments on them, as well as access them from any of your devices. Evernote will even recognize your handwriting so you can easily search for notes. Also available on Mac. (Free)

Cloud storage is everywhere these days, but Dropbox is king. Back up and store files you can work on collaboratively with coworkers and access on any of your devices. Dropbox is also a quick and easy way to move files between your computer and your device. Dropbox storage starts at 2GB for free with additional storage for referrals or purchase. (Free)

Like we said, cloud storage is everywhere. What makes Google’s version so special is the ability to create and edit Google Docs on your devices. Perfect for working on-the-go and collaborating with coworkers. (Free)

Lift is designed to help in the formation of good habits. Enter in the habits you’d like to build (floss, exercise, check the news, read, etc.) and check them off as you complete them. It will even remind you to complete them. Lift keeps track of how often you complete your good habits and displays helpful data so you can monitor your progress. (Free)

As we said earlier, there are those who don’t think the built-in apps are powerful enough. For those that would like a better alternative to Apple’s built-in Mail app, Sparrow is the app for you. Not a radical change from the email clients you’re used to, but Sparrow’s small tweaks make it easier to work your way through that crowded inbox. Also available for Mac. ($2.99)

If you work with a lot of pictures, blueprints, etc., Skitch will save you a lot of time and help you communicate visually in the digital world. Edit, markup, and annotate images and screencaptures easily so you can get your point across quickly. Also available for Mac. (Free)

Expensify is the best way to manage your business spending across your accounts and devices. Especially useful if you travel for work a lot. The app keeps track of all your credit card transactions, paper receipts, and mileage (using GPS). Expensify then automatically generates an expense report as a PDF. Simple as that. (Free)