Khmer Idea Restaurant is in Pub Street and they are open for breakfast, lunch and dinner. You can also order picnic boxes for that big day out.
We visited here quite a few times and their meals are fresh, tasty and cheap. There is also an extensive cocktail menu and all cocktails are $4 each but buy one get one free, Angkor draft was 35 cents a pint and I have to say they make the best White Russians I have had in Cambodia.
Good spot for a rest and people watching.