Here's some interesting and funny Japanese onomatopoeia:

sound of a small dog "kyan kyan"
sound of a large dog "wan wan"
sound of a cat "nya nya"
sound of a rooster "kokekokko"
sound of a pig "buu buu"
sound of pouring rain "zaa zaa"
sound of a heart in love "doki doki"
a mess all spread out "bara bara"
something old and delapidated "boro boro"