The OP didn't specify time of year or ages, so I'll just put them out there:
- Summer, music in Princess Park
- year round - library has speakers come in from time to time, also they sometimes show films usually NFB films
- Sept thru April - Evans theatre at the university, I think tix are pretty cheap, they show lots of TIFF stuff & art films, stuff you won't see at regular theatre
- public skating at Sportsplex is $7.00. There might be days/times that are cheaper like how swimming there used to be on Tuesdays & Fridays
- BU School of Music often has concerts for a reasonable amount, usually about $15, student recitals are often $5-$10
- tons of walking trails (year round)
- fire pits at Queen Elizabeth Park & Dinsdale Park still open, firewood is usually provided but you'll have to check things have been a bit dicey in recent years with all the flooding
- If you have a car, the Brandon Hills just south of town are spectacular this time of year
- check out the events page on ebrandon & the listings that come in the community news with your flyers
- if you're a BU student, you have a membership to the Healthy Living Centre included in your fees
- Art gallery is free, they also have art classes that are fairly reasonable cost
- Funtime Pottery often has specials, I think Thursdays are ladies' night
- BU observatory is open to the public some nights. There's also a local astronomy club that has recently started.
- Wheat Kings have 2 for 1 Tuesdays (see
http://www.wheatkings.com/page/2-for-tuesday)
I could keep going.