This little program will allow you to make a playlist in the .m3u style by simply dragging and dropping one or more music files (.mp3 or .m4a file extensions) or playlist files (.m3u file extension) onto it, you can't (yet!) drag and drop folders, you can then randomize or sort the playlist and then save it, it will be saved as a plain text file with the .m3u extension, if you don't add .m3u to the file name it will be added for you.
Although this prog was written primarily for Rockbox the file type is used by a number of different music players and so should be pretty universal.