WAV

WMP supports the WAV format.
It won't write tags in WAV (with one minor exception, see below)
Bit funny as this format is co-invented by Microsoft and IBM and technically you can write almost anything in RIFF chunks.
If you move the WAV's from your local HD to a another computer probably all meta information will be lost as it is stored in the library only.

More about WAV can be found here.

RIFF

Only when ripping a CD to WAV a couple of RIFF Info Tags are written.

You can't change them afterwards.

The tags are:

IART (artist)

INAM (title)

IPRD (product)

IGNR (genre)

ITOC (?)

ITRK (track number)

Thanks to ZachD