There are many places you can enjoy the popped stuff around town... namely movie theatres!

DOWNTOWN > City Centre Movie Theatre
It's run by Landmark Cinemas, so there are lots of Hollywood blockbusters screening. You've got 9 different movies to choose from.
You can take public transit to the mall, including the LRT.

GARNEAU > Metro Cinema
Grab some VERY affordable popcorn before watching an arthouse film at the historic Garneau Theatre. *No extra charge for butter at this place!
The longstanding landmark is home to the community-based non-profit society devoted to screening Canadian, international and independent film and video.

QUEEN ALEXANDRA > Princess Theatre
With two screens, there's always various quirky, mostly indie films in rotation.
There's popcorn machines one each level of the theatre. So regardless of which theatre you opt for in the building, there's popcorn ready to enjoy.

If you don't mind celebrating a day late...
OLD STRATHCONA > Old Strathcona Farmers' Market
Head to the old bus barns to get a generous dose of freshly popped kettle corn