Google has released Google Mobile App for Windows Mobile. Google Mobile App gives you faster searching on your Windows Mobile device, with easy access to your favorite Google applications from the Today screen. There's no need to wait for a browser to open to begin a search, and with search history available to reduce typing, you can get your search results with fewer clicks than before. For an even speedier experience, Pocket PC users can add the Google Mobile App to the start menu (Settings: Menus) or configure a hardware key (Settings: Buttons) to provide easy access from within any application on your phone.

According to Google Mobile blog, Google Mobile App is available for all devices running Windows Mobile in the US, UK, Canada, France, Italy, Spain, and Germany.
Google Mobile App can be downloaded from http://www.google.com/mobile/winmo/, or directly download to the phone from http://m.google.com/search.