[Nokia Lumia 900] DoogieDC:
I have gone from an HD7 to the HTC Radar, and now the Lumia 900. Here is what has earned their keep in my Windows Phones:

Communication & Security

Freetalk - is a Google voice client. I couldn't indulge in my multi-phone, multi-carrier, multi-phone number lifestyle without Gogle Voice.

Rowi - a very full-featured Twitter client.

Skype - it's official! Version 1.0 was released on Friday. The Lumia 900 is great for Skype with the front camera.

Skydrive- this should be on every Windows Phone by default. 16 gb memory limit got you down? No problem! Set all your photos to automatically upload to Skydrive. Move downloaded files on to Skydrive.

LastPass - Password manager, (like 7 Pass). THe program is free to use on your Windows and Mac desktop, but you have to subscribe ($25/year) to use the mobile clients (WP7, iPhone, Android). I like it because it will fill out all passwords for me, generate secure new passwords, and store other secure information (credit cards, software licences).

Photo & Entertainment

Creative Studio - another great Nokia freebie that handles basic picture editing tasks (crop, exposure, color, contrast) as well as some artistic filters you can apply.

Picasa Metro - a client for Google Picasa Photos web service. I can upload pics from the phone to my Picasa folders, and use my Picasa pictures for things like backgrounds on the phone.

Fandango - see what's playing in movie theaters near you and buy tickets.

Netflix - a must have if you are a subscriber.

Vevo - primary site for music videos.

BBC Radio Player - listen to live BBC broadcasts. I am a big fan of programs in BBC 1, BBC 2, BBC London, and BBC Scotland. This plugs me in to those progams and all the goings on in the UK.

Reading

Weave - a deluxe RSS newsreader. Even if you don't have feeds that you follow, Weave lets you just point to subjects in which you are interested and it pulls in the top feeds for that topic. For example if you check the topic "Windows Phone" you will get Engadget, WMPoweruser, WPCentral, and others. You can uncheck any specific feeds in which you are not interested. This eliminates the need for individual reader apps (CNN, USA Today, Engadget, etc.) and gives me a single place to read everything. At the other end of the scale, you can import your entire Google Reader subscription list.

XDA-Developers - duh!

XMarks - all my bookmarks from my desktop are here on the phone.

Amazon Kindle - all my books available here.

CNN, ESPN, USA Today, Engadget, WPCentral - these are all well designed news apps with live tile support.

Shopping

eBay - A must-have for e-bay buyers and sellers.

Amazon Mobile - great for impulse buying new gadgets you read about in Weave!

Misc

Nokia Maps and Nokia Drive - Hey fellow Windows Phone owners, we have great turn-by-turn directions for FREE from Nokia, so neener, neener, neener! ;)

Evernote - I couldn't work without this multi-platform note taking / web clipping application. Whenever I find something on the web that I might need later I paste it into Evernote and add subject tags. That way I can pull it up any time in the future. There are versions for WP7, iPhone, Android, Nokia Symbian, Windows desktop and Mac. All information is kept in sync between all your devices.

Timer - it's just a timer, like you have on your stove or microwave. But I use it all the time for cooking and knowing when to take the clothes out of the wash.