We'll warn you right off the bat, if you have been waiting for a Google Search App for Windows Phone, it's now available, but it probably isn't really what you have been waiting for. Google has released version 184.108.40.206 into the Marketplace, but there really isn't much to it. Probably the only feature that it has over what you would get if you went to Google.com in your browser is the option for voice input.
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.