So you just created your first multi-platform app. Now you find yourself looking all over the Internet for some decent marketplace / store / play icons.
Search no further. Here are the links to the official images.
Windows Phone marketplace


http://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=5014
Also contains the illustrator files and generic phone images in photoshop format.
iOS App Store


https://developer.apple.com/appstore/resources/marketing/index.html#agreement
After login with apple Id, you can find badges in any language and device images in various formats.
Android's Google play


http://developer.android.com/distribute/googleplay/promote/badges.html
This is more a generator then a simple download. Contains the latest Google play badges, but also Nexus device images. The generator allows you to drag your own images onto the devices and generate youre own marketing images.
Windows Store


http://msdn.microsoft.com/en-us/library/windows/apps/jj670536.aspx
Also contains some great tablet device chassis downloads.