If you're a news feed junkie (you are subscribed to the TrustedReviews feeds, aren't you?) then you'll want a decent RSS news reader app for your phone. NewsGator Go! is one of the best around because it integrates with the online NewsGator service. You create an account online and use the web-based interface to select the feeds you want to track. Then it's simply a matter of entering your username and password into the NewsGator Go! software to have your feeds sync to your mobile. The navigation is excellent and you can also clip articles to store them for reading later.
If you're a heavy user of Gmail, then chances are that you also use its calendar function to remind you of meetings, birthdays and other important appointments along with its online contacts book. Well, guess what Google Sync is for? Yes you've got it. It's a simple, no nonsense way of synchronising your Google calendar and contacts to your Windows powered smartphone. That's pretty much it, but for some it'll be a crucial addition to their smartphone.
Google Mobile - Sync
Dashwire is a web service that lets you back up your contacts, text messages, photos and videos online and then access them via your computer's web browser. However, there's more to Dashwire than merely backing up data; it also lets you share photos and videos with friends or send them to Flickr or Facebook accounts. There's also a cool messaging app built in as well as lots of other goodies.
Orb Networks Orb
Orb isn't exactly a native Windows Mobile application, but it works brilliantly with Windows smartphones so we're taking the liberty of including it here. The application actually runs on your desktop PC, but the clever bit is that you can use it to broadcast the media content stored on your PC across the Internet to your smartphone. The key to the system is that the Orb software on your PC transcodes files on the fly to make sure they're playable on your handset.
Shape Services IM+
If you make heavy use of instant messaging then you've probably got different friends using different services with the result that you have to either mess around with multiple clients or plumb for a unified instant messaging app instead. If you want to take the latter route then IM+ is a great option. It currently works with a pretty comprehensive range of IM services including iChat, MSN Messenger, Yahoo! and Google Talk. There's also a handy IM+ panel available for the Sony Ericsson Xperia X1 handset that can be used to display unread messages.