I've evaluated Zenoss before, but forgot the default password, and searching for it didn't come up with anything quickly. I tried everything under the sun: password, 1234, admin, God, Sex, but alas, grep to the rescue:
kelvin@monitor:/usr/local/zenoss/zenoss/etc$ grep admin * hubpasswd:admin:zenoss
Update: it is listed on page 4 of the Admin PDF :)