Google releases Search App for Windows Phone
Other than that, it is a simple search box with Google's autocomplete on search suggestions. The app also can use your GPS (with your permission of course) to give you local results. That's really about it. It is the basic Google UI, nothing Metro about it, and that's it. Not the strongest showing from Google, but maybe that's all you need.
If so, you can get the Google Search App for free in the Windows Phone Marketplace.
source: Google Mobile Blog