I took my parents-in-law on the HIPPO River Cruise today and it was quite enjoyable. For half an hour we cruised down the river from Clark Quay to the Merlion and back. I liked seeing Singapore from a different perspective, and the guide, who annoyingly kept referring to us as "my friends" was not too overbearing.
Here are some photos of the short tour:
HIPPO River Cruise
Admission: $15/ Adult, $9/Child (3-12yrs old)