take allways mp3(music) and divx/xivd(opensource), mpg/avi, mp4, 3gp -these standard codecs are working most of other devices...

Divx/xivd needs not much space and is similar to wmv.
music video clib are 5 - 9Mb (3min to 5min length)
90 min Movie around 150Mb to 300Mb (depends what quality you want).
divx/xivd converter = virtualdub(freeware), stoik videoconverter(freeware) and others..

less space than wmv you can have with the .rm real-codec.when compare the picture quality with wmv.
.rm converter = easy real producer (freeware)