There is also the "p" series:

pa  pi  pu  pe  po

I would also add the following ones, since they are not exact sums of the previous sounds. They are written with two kana, where the second one is smaller:

kya kyu kyo
gya gyu gyo
sha shu sho
ja  ju  jo
cha chu cho
nya nyu nyo
mya myu myo
hya hyu hyo
bya byu byo
pya pyu pyo
rya ryu ryo

You could also add special syllables which were created for foreign words and are usually written with katakana, such as vi, fe, etc.