Best Apps Market

Nice app to discover good apps and games. Check also App Sales.

Best Apps Market @ Google Play

Timpik

Brilliant service for organizing sport events with your friends or other people. Join an event or organize one. If you like to practice sports you will love it!

Timpik @ Google Play
Timpik @ the web

Duolingo

Fun app to learn languages. It uses gamification so you earn points and advance through levels. They also have a web site.

Duolingo @ Google Play

Duolingo @ the web

Trello

A great organization tool that takes your TODO lists to a new level. Lately they added a feature to add items (cards, they call them) from email. You might also like Wunderlist 2.

Trello @ Google Play
Trello @ the web

AppSales

Lets you discover apps on sale. You can add some apps to your watch list so the app notifies you when their price drops. I've experienced some issues but nothing important. Take care because you may end up buying a lot! :-)

AppSales @ Google Play

KeePassDroid

Useful app to store your passwords. It's the Android version of KeePass.

KeePassDroid @ Goolge Play

Chrome Browser

Fine browser with many useful features. For example, it zooms when you click between two small links, it has a fun way of managing tabs and also lets you sinchronize your tabs between your mobile and desktop.

You may also want to try Dolphin Browser and Boat Browser.

Chrome Browser @ Google Play

AppBrain Ad Detector

This app lets you see information about your installed apps: concerns, ad networks, social SDKs and developer tools. Concerns section tells you if your apps can access your contacts or accounts, may cost you money, can access sensitive data, etc.

AppBrain Ad Detector @ Google Play

Evernote

Great note manager that stores your notes online. It also has a desktop (Mac/Windows) app and a brower app. It's not perfect because you can't edit notes with complex formatting from your phone, but it usually works very well.

Evernote @ Google Play

Wunderlist 2

Nice TO-DO list manager app/widget that also lets you access your lists from a browser and stores your data online so you don't lose your TO-DO's when changing your phone. Check out Trello too.

Wunderlist 2 @ Google Play
Wunderlist 2 @ the web

Digital Clock Widget

After trying several clock widgets I chose this one beacuse it is simple, displays both the date and the next alarm, and lets you open your favourite alarm program when you tap on it.

Digital Clock Widget @ Google Play

Nova Launcher Prime

This launcher lets you customize many aspects of your desktop and app drawer. I like the gestures, the app groups and how you can increase the rows and columns of your desktop and resize your widgets.

Nova Launcher Primer @ Google Play
There's a free version here

Business Calendar

This is my favourite calendar. I especially like its widget and how easy it is to add/edit events and see my different Google calendars (work, personal, etc) in custom colors.

Business Calendar @ Google Play
Check out the paid version for more features.

SwiftKey keyboard

I've tried several keyboards and this one is my favourite. You can type or slide/swipe, it predicts your next word and improves with time by learning from you, and it's not necessary to select the language you want to write in.

Swiftkey keyboard @ Google Play
Trial version here

JAYS Headset Control

Many headsets have 3 buttons but only one of those buttons work for Android. This app is the solution. It lets you control everything with just one button: pause, skip, change volume, etc.

EDIT: This app and others have problems with long clicks in Jelly Bean, but it's Google's fault. There's another app called Headset Button Controller that has an option to change volume by increasing it until you stop it. Not very handy, but it's the only solution (besides rooting the phone) until Google fixes the problem.

JAYS Headset Control @ Google Play