Rochester Park is lovely - a few restaurants there eg. Graze, One Rochester, Da Paolo. Graze is my favourite.
Also, along Chip Bee Gardens in Holland Village is really nice at night - Da Paolo and Michalangelo both serve good Italian food and Original Sin is a great vegetarian restaurant. Outdoor table preferable I think (weather permitting).
Flutes is also excellent. As is Broth on Duxton Hill, Oso on Tanjong Pagar and Senso on Club Street. Would recommend Singapore's Best Restaurants 2008 book which you can get in Borders or other bookstores. It's really handy.