A nice thing about B&W G3 and Yikes G4 is that they are the last macs with the older style ADB connectors for keyboard and mouse. This expands your options also beyond USB hardware from windoze machines. You can also use the nice ones from older macs. On my B&W G3 I used an old large mac keyboard which i found thrown away, it is called Datadesk 101e and is one of my favorites I have ever used.

I would caution against beige G3s for Mac OS X because they only run older versions, and have firmware problems.