I've put together a (7-part) video tutorial that shows you how to get your Wii Remote working in Unity Indie. In short, I send data from the Wii Remote to Flash, and then these data are being passed to Unity.
So the tutorial covers two things:
Exchanging data between Flash and Unity with U3dObject
Hooking up your wiimote with WiiFlash
If you don't have a wiimote or are not interested in the wii part, the video may still be worth watching if you want to know how to set up communication between Flash and Unity; something that could serve many more purposes than just the wii thing.
The videos discuss only the Wii Remote, but hooking up your Nunchuck is just as easy. Also, the balance board is supported by WiiFlash.
The tutorial got a little longer than I had in mind - total running time is 55 minutes - but if you have a Flash or/and Unity background, you may want to skip forward here and there.
I have bundled two example projects, which you can find here. I included the simple project from the video tutorial, and also a second project, which demonstrates how to hook up the Wii Remote and Nunchuck to Unity's FPS_Tutorial.
UPDATE: In the video I say that the latest mac version of the WiiFlash server - 0.4.5 - was not working for me. I have tried it again, and now it seems to work fine - not sure what happened last time. Keep in mind though that you may have to tell it to open in 32-bit mode. Right-click on the app, select Get Info and check the Open in 32-bit Mode checkbox.