Ajisen Ramen's always one of my favourite's

It's a chain, so you can find it anywhere, but the airport has one and I know that Sheung Shui has one too.
Cafe de Coral is where we literally go everyday for breakfast, lunch and dinner when I go to HK because it's just so cheap and the food's delish (try the ice lemon tea as well, 'cus i'm a biggg fan :P)
Oh, and I've been to the R66 revolving restaurant and the buffet there is really nice. The scenery you get and the atmosphere is memorable too
But, yeah, anywhere you go has nice food