* Rarely: This is the most common opposite and implies something happens infrequently.
* Seldom: Similar to "rarely" but emphasizes the infrequent occurrence even more.
* Never: This means something has never happened.
* Occasionally: This means something happens sometimes, but not frequently.
* Always: This is the complete opposite if "often" implies something happens frequently, but not always.
Example:
* Often: I often go for walks in the park.
* Rarely: I rarely go to the movies.
* Never: I never eat spicy food.
The best opposite for "often" will depend on the specific meaning you want to convey.