I have been to a lot of diners in Calgary mainly because breakfast is good no matter what time it is :)
Located in Mardaloop, this one has a great 50's neighbourhood feel! The food is great! Prices are reasonable, portions are huge and they serve bottomless hash browns, need I say more? I will anyway... Don't be discouraged by the long lines in front, it usually moves quickly and they will bring you out coffee to keep you warmed up. Staff is awesome and you see very few new faces behind the counter... I've been looking at some of them for 7 years now, and that is a long time for this industry!
Be warned though... It is only open until 4 pm :( Too bad... 24 hours of this place would be the best gift we could get...