Usually I was working with BING`s Visual Search to search for products like DigiCams or Album Covers. If I wanted to search through the WindowsPhone Marketplace and did not have my ZUNE-Application running, then I checked nice websites like AppsFuze, WP7AppList, WindowsPhone7 Apps, AppHub or MarketplaceBrowser for new apps. Now BING is offering a quick and easy visual search through the Marketplace.
Just change your BING-country settings to "US-English" and click on this search query.You can drill down in the category section and search only for Business Apps or Games. Top Navigation can be used to filter for 25 top rated Apps or 25 newest free Apps. In the left top section, closed to BING logo, the amount of Apps in the Marketplace is mentioned.
EDIT: it is also possible to search for iPad und iPhone-Apps, see here Now there is an offical BING Blogpost available here