Somewhere in the dustbin which is my brain, I recall discussions here about the various words used in different cultures to mimic animal noises. Here is a site which reproduces animal noises, as performed by children from different countries:

http://www.flat33.com/bzzzpeek/index1.html#

The site also provides sound files for some inanimate objects, like trains and such, as well as one human utterance.

Sheep, it seems, have a limited vocabulary.