I just did a quick google and found this site:
Shadow Poetry -- Resources -- Haiku and Senryu
and this one which adds on some stuff about a type of japanese poetry called 'Renga'
http://library.thinkquest.org/C0126526/history.html
and of course, wiki has plenty to say on the subject:
Japanese poetry - Wikipedia, the free encyclopedia
Fuuu~ there's a lot more to Japanese poetry than just the haiku, that's for sure!