Laura posted this list compiled by mobile.blorge.com in Third-Party Software, and I thought it would be nice to have it here, as well. I'm sure not everyone will agree on this exact selection as being the top 40, however, so please add your own.
AIM Mobile - Featuring a slick User Interface, color emoticon support, and support for Windows Mobile 5 and 6, this app is like having AIM's desktop IM client on your phone. To get the Windows Mobile client: In your web browser on your cell phone, go to http://wap.aol.com/portal/menu.do?id=5705 click on "AIM", then from the drop down menu select "AIM for Windows Mobile!"
Dashwire - This app lets you back up your phone's contacts, text messages, videos and photos online where you can access them using your PC's web browser. The app lets you share photos and videos or upload them to your Flickr or Facebook accounts.
File Explorer Extensions - Here's a great alternative to the default Windows Mobile File Explorer. This app features resizable headers for easy sorting by file name, date of last modification or size, tree view of folders, and icon views. In addition, the app offers an image preview function.
FingerSuite - This app is a cool alternative to the standard menu and message box on Windows Mobile phones. It provides attractive and easy-to-use menus.
FlashLight - Who says only the iPhone can turn into a flashlight? This app gives you access to various light applications including LAMP, strobe, fader, disco, pen, lighter, and more.
Google Sync - If you're a fan of Google's web services such as Gmail, Calendar, and online contacts manager, then you'll want this app. It syncs your phone to all of your Google accounts.
Group SMS - We are all fond of sending messages to multiple recipients, right? Group SMS makes it easy letting you send a text to a large group without keying in phone numbers one by one.
GSPlayer - This app is a great way to manage your MP3s.
HelloTwitFace - This is one of the best looking Twitter clients for Windows Mobile phones, letting you view and update your Twitter and Facebook status.
iContact - This is an intuitive Windows Mobile contact chooser that supports VGA skins of any screen size.
iDialer - This app serves as a dialpad for your phone, allowing you to make calls using your virtual number from Google Voice/Grand Central, Phone.com or Jajah. The app features various interchangeable skins and supports VGA and QVGA skins in both portrait and landscape modes.
iFonz - If you don't want to get an iPhone but want to experience its home screen interface, then you might want this app. If doesn't offer any new functionality outside of replicating the appearance of Apple's phone.
iPlayer - This app lets you browse and stream contents from BBC's iPlayer. It features a finger-friendly user interface and lets you browse content by highlights, popularity, category and more.
Kevtris - Looking for a nice little game to play on your Windows Mobile phone? This Tetris hybrid can be addicting once you get used to using your phone's small buttons.
Magic Button - This task management app is located on your phone's title bar. It hides automatically when you don't need it and blends well with your phone's theme.
mDigger - This app is similar to a mobile RSS reader. It also allows you to select the format of those feeds - text, images, videos or podcasts - and tailor-fits content to your phone's screen.
mLock - This phone lock app starts running the moment your phone goes to suspend mode. You can customize its function and its appearance. The app features portrait and landscape orientation, supports QVGA and WQVGA resolution and more.
MobilePad - This light and speedy text document editor that lets you create quick notes and long journals. This app also lets you exchange files or text messages. It features auto-save, landscape mode, text zooming, search and replace capability, and more.
MSN Direct - Since we're talking about Windows Mobile app, a Microsoft app should be on the list. MSN Direct sits right on your phone's home screen and gives you access to up-to-date news, stocks, and weather information all coming from the MSN website.
MyMobiler - Want to remotely control your WinMo phone? Then this app is a must download. With it you can use Active Sync connection to remotely access your phone from a computer.
Newsgator Go - This is a good RSS news reader app that integrates with the online NewsGator service. The app features good navigation interface and the ability to clip articles for reading later.
Opera Mobile - This is a great alternative to the default Microsoft Pocket Internet Explorer. It offers faster web browsing and better panning and zooming.
PDAcraft Paint - If you have a touchscreen Window Mobile phone, this app is a fun download. You can draw directly on your phone's screen using a stylus and manipulate bitmap graphics in the same environment as the popular Paint program.
PhoneLog - This simple app records all your calls (including their duration) on the phone's calendar. It also logs incoming SMS messages.
Pocket Digital Clock - A better alternative to the default Windows Mobile default digital clock, this app offers a larger, easy-to-read white-on-black digital clock display that sits atop your phone's Today screen.
Pocket DivX Player - Pocket DivX Player lets you play DiVx, Mpeg-4, Mpeg-1 videos, Mp3, and OpenDivX video formats. The app features a 10-band equalizer, a playlist editor, playlist support, web streaming, brightness control, and more.
PocketCM Keyboard - The iPhone's finger-friendly virtual keyboard is great. But who says you can't have the same on a Windows Mobile phone? With the help of this app you can compose text messages and do other things using your phone's screen.
PocketQuake - Who could ever forget the classic game Quake? Certainly not the developer of this Windows Mobile game. This pocket version is reminiscent of the original 3D shooter game, replete with quality graphics and addictive gameplay.
PocketRAR - We all need a pocketable file extraction utility on our phone, and this app fills that need well. It offers a good graphic interface and can compress, decompress and delete files in both RAR and ZIP archives.
Pointui - This app makes your phone's interface simple and fingertip friendly. It increases the size of your phone's home screen icons allowing you to access the phone's functions quickly.
Scrub - This app lets your detect missing information like email addresses, phone numbers and birthdays from your contacts by quickly scanning your phone and groups the information to let you identify what is missing from your contacts' entries.
SKTools Lite - This free version of SKTools lets you delete old or obsolete files, cleans your phone's registry, fixes shortcuts, and frees vital RAM.
Skyfire beta - A free version of the powerful Skyfire app, Skyfire beta lets you watch Flash videos, listen to music, and enjoy a desktop interface on your phone's screen. It also supports AJAX, Silverlight and Quicktime formats.
Skype - Before the Skype iPhone app, there was the Windows Mobile version. Use it to make voice calls over Wi-Fi, free Skype-to-Skype calls and affordable landline and mobile phone calls.
Slick - This app lets you send instant message through Google Talk, Jabber, AIM, ICQ, MSN and Yahoo. It also features text messaging, emoticons, message history and more.
SmartTouch - This is a mobile widget platform providing seamless access to branded content and services including Facebook and Google. It features a simple scroll-and-click text messaging system shortcuts.
ToneThis - Use this app to create customized and unlimited ringtones from your CD, MP3, WAV, iTunes, and video files.
WorldMate - If you're a frequent traveler, you'll find this app very useful. It features Itineraries Manager, which provides information on flights, meetings, public transportation, car rentals, and hotels. It also lets your import booking confirmation e-mails from your PC to your phone.
YouTube Player - YouTube fans will certainly enjoy this. The app features a minimalist interface suitable for a small screen.