XDA forum member pikipirs has developed an app that allows you to use a Wiimote as a controller on your Android-based phone.
and a video of it on a Nexus One:
Now here’s the bad news. It won’t work with any HTC devices that feature SenseUI, even if you turn it off. There’s a bigger problem somewhere and he hasn’t figured it out yet. However, since the app is currently in an “alpha” stage, it’s to be expected that everything isn’t working 100%.
But if none of that scares you, then search for “Wiimote Controller” in the app market, or head over to his forum post for the APK’s.