The equivalent of the C:\Windows\Fonts folder within the current Wine prefix.
This is where you should manually copy self-installed fonts, either downloaded from the Internet or copied from a Windows install.
The ~/.fonts folder in your Home directory.
Examples of these fonts include Wine's private marlett, symbol, and tahoma fonts, which are needed for application compatibility but otherwise aren't the best. You shouldn't add fonts here, but if you see a font in Wine and not in the system - it's probably here.
Wine's private /usr/share/wine/fonts folder.
You can add fonts here by installing font packages from Software Center, if they're available.