Not sure what your budget is but I like Gaia in Sheung Wan - the same group as Isola in IFC but much smaller and romantic. I also like Verandah in Repulse Bay, Cafe Gray in Admirality,and if you have a bigger budget Hutong in TST. Zuma is also nice for Sunday Brunch buffet but I wouldnt call it romantic plus it's quite expensive.
Bistecca in Lan Kwai Fong is really nice, it's a steak house though so obviously only good if you're into steak! Also 208 Duecento Otto is very nice and maybe a little cheaper.
The French Window at the IFC is uber romantic, but it's definitely for a special occasion budget. If you go, make sure to reserve a window seat, or one of the banquettes for side by side seating! I love the complimentary champagne cocktails as you take your seat.