I think there's a special ticket for 1 admission each to the Zoo, Night Safari and Bird Park for about S$45, valid for 1mth. That's a pretty good deal if you're planning to visit all 3 places.
By the time u're here, the Sands Casino will also be opened. So u may want to check out both Casinos since u'll get in for free (as compared to Singaporeans) and their surrounding eateries. I think the Universal tix is about $60-80/pax depending on weekdays or weekends.
I think Clark Quay will be more interesting as Boat Quay is kinda sad and old looking nowadays. Take a bum boat ride down the Singapore River or go on the Duck Tour or hop on the Hippo Bus. Both can be found at Suntec City.
There's a Glutton Square next to the Esplanade with famous hawker stalls that you can check out too. Of cos the world famous Orchard Rd for the shopping (4 new malls opened in the last 6 mths) and Sim Lim Square for the electronics.
If you want a bit more local flavours.. go to a housing estate like Toa Payoh or Ang Mo Kio or Tampines. Easily accessible as the MRT stops right in the heart of these places.
Check out the National Museum if u want a look into the Singapore history, or to the Asian Civilisation Museum if you want history relating to the local culture.
Just shop and eat your way through Singapore. =)