With over 1000 apps in the Windows Phone Marketplace that use new features in Windows Phone 7.5 Mango (and over 42,000 apps in total), there's plenty to choose from.

We had a hard time narrowing this down to our 20 best free Windows Phone 7.5 apps, even leaving out pay-for apps like the excellent Thumba Photo Editor.

Here are our favourites that make the most of background tasks, secondary live tiles, access to the camera and other Mango improvements, or apps that make the new features in Mango more useful or easier to use - and they're all free.

1. Spotify

It's not just a bit of a landmark app for the Windows Phone platform, the Spotify app is excellent in its own right (especially on a handset like the Lumia 800 with good speakers).

Enjoy playlists you've already set up, search for tracks to listen to or add them to a specific playlist, or listen to friends' playlists.

You can stream tracks or save playlists to your phone to listen offline, you can go back and see what you've listened to recently, and while Spotify has its own player with options for sharing and starring tracks you can also use the standard Windows Phone volume and play controls without switching back to the app.

The what's new albums aren't limited to the six tiles you can see on screen; keep hitting refresh for another selection. About the only option from the desktop client we can't find is being able to rename a playlist; new playlists get the name of the first track, album or artist you add.

Spotify

2. Evernote

If you prefer Evernote to OneNote, the Mango update is crammed with improvements to make iPhone users jealous, including Wi-Fi background sync of your notes; you can pin specific notes, notebooks, tags or searches to the Start screen.

You can pin templates which can include tasks like taking a photo and saving it as a note with some boilerplate text - ideal for recording receipts, business cards, wine labels or anything similar. And when you search on Bing, you can swipe across for a list of matching notes in Evernote.

Evernote

3. Tango Chat

Until the Skype and Lync apps come out, Tango Chat is the only video chat for Windows Phone and it's available on a lot of other platforms already so you probably have friends using it.

It's easy to find out as anyone in your address book using Tango shows up in your contact list automatically. Call quality is good; it works best with a front-facing camera but it still works without one (as long as you only want to either see or be seen but not both at once).

Tango chat

4. EasyRing

Mango lets you have your own music as ringtones. Rather than cutting MP3s down to 50 seconds and copying them through Zune by hand, use EasyRing to find free ringtones online, try them out and save them to your phone (two separate steps, by the way).

You can also download any MP3 file you can find on the Web and crop that to length on the phone. Although this app has a price tag, the free trial has all the features and the developers invite you to use and pay if you like it.

Easyring

5. Flickr

Being able to upload photos directly to Flickr is handy (although this can be infuriatingly slow) but what's most useful in the Mango update of the official Flickr app is being able to pin live tiles for your photostream and for updates from friends who haven't linked their Flickr account to Windows Messenger (so new pictures don't show up in the What's New page).

Flickr

6. Facebook

Windows Phone already has a lot of Facebook integration - Facebook events show up in your calendar, you get contact details, status updates and photos from friends.

The Mango version of the official app has a clean and simple Metro interface for getting more details, including a nicely tiled picture section. Most useful is being able to pin the Messages section as a live tile, instead of relying on email alerts; you can also pin Places to keep track of friends as well as Events and the News Feed.

Facebook

7. 4th and Mayor

The official Foursquare app lets you pin live tiles for 'places' and 'specials' and it supports multitasking so it's faster to switch back from other apps, but we prefer 4th and Mayor which has much nicer live tile options.

As well as pinning CHECK-IN NOW to your Start screen, you can pin tiles for your favourite places and friends you want to keep track of - and you can choose the title and image to use for them.

4th and mayor

8. Seesmic

Both the official Twitter app and the reliable Seesmic have Mango updates and despite the built-in integration you'll want an extra app for direct messages, reading lists and quoting tweets.

Seesmic has the edge with fast app that switching means you don't lose track of where you are in the stream of tweets when you switch to another app, and you can pin live tiles for replies and direct messages. If you're prepared to pay, we'd also recommend Rovi.

Seesmic

9. INRIX Traffic

Bing Maps shows you traffic levels; INRIX shows you far more detail, including roadworks and events that can cause traffic blackspots - and it can predict what the traffic is going to be like on a road when you drive it later in the day.

The Mango version lets you pin a map area to the Start screen, so you can keep your journey home at your fingertips.

Inrix

10. Yapf

Prefer Google's database of places to Bing Local Scout? Use Yapf to search Google - and see the places on Bing, complete with directions, or get an augmented reality view that overlays the results on the view in front of you, so you can see which of the pubs you can see in the distance is the one you're heading for.

You can also pin a place to the Start screen so you can keep an eye on the distance or get back to the directions quickly - great if you think you know the way but want to check it as you go.

Yapf