See available drives from Windows CLI?

> wmic logicaldisk get caption

Caption
C:
D:
E:

if probably the easiest one. Doesn't need administrative privileges, doesn't return more or less than what's needed, etc.

If you want to use it in a script, then wrap it in for /f with the skip=1 option:

for /f "skip=1 delims=" %%x in ('wmic logicaldisk get caption') do @echo.%%x

If you're in Command Prompt:

diskpart

then

list volume

sample output:

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0     E                       DVD-ROM         0 B  No Media
  Volume 1         System Rese  NTFS   Partition    100 MB  Healthy    System
  Volume 2     C   System       NTFS   Partition     99 GB  Healthy    Boot
  Volume 3     F   Data (local  NTFS   Partition    365 GB  Healthy

and finally

exit

to return to the command line.

For the sake of completeness, there is yet another way:

fsutil fsinfo drives

which returns:

Drives: C:\ D:\ E:\ F:\

(Not a very scripting-friendly output, but it may be useful for human eye)

Some reference. That should work since win2k but only with Administrator account.

(Thanks @Carlos Campderrós for enhancing the answer)

If you're using powershell then you can type in

get-psdrive -psprovider filesystem

Edited in response to comments to only show filesystems