It seems guaranteed that Windows Phone 7 will launch with quite a few games, but that is still a few months off.
Fortunately with much of the software on Windows Phone 7 running in Silverlight, the resulting emulator app can run as easily on the web.
DroppyPop is a Windows Phone 7 game by Spritehand where you control a rag doll which is falling through an endless sky of balloons. The purpose of the game is to pop as many balloons as you can for points while avoiding the bombs and baddies along the way.
We will have to wait for the Windows Phone 7 version, but the Silverlight version can be played right now, right here. (See if you can beat my high score!)
Read more about the project here.