Was in Ottawa over the weekend, and dined at Domus based on the positive reviews posted here. I will definitely eat there again the next time I'm in Ottawa. Lovely place - no ostentatious decor, no music, just seriously good seasonal food at un-Toronto prices. I had a cold chili/miso/pureed green pea soup - wow! It was followed by a yummy grilled duck - generous portion, too. Didn't have any room for dessert.
The next day I hankered for a greasy breakfast and stumbled into Mello's on Dalhousie St. in the Byward Market area. I don't recall this place being mentioned on this site, but I found it very cheap and satisfying - and it's open 24 hours!
Thanks to everyone who recommended Domus.