According to some posters I saw on the wall, the end of term concert for the University of Waterloo's acappella groups is July 23rd at 8:00 PM in the Theatre of the Arts. I don't know if I'll have time to go, but it should be fun times!
EDIT: Oh, hey, also: it turns out that July 23rd is also the day of the Engineering Jazz Band Charity Gig! Yayyyyy. The jazz band will be playing sometime around 6 PM (I think, details coming) at Waterloo Town Square. As a member of the band, I will probably be there. See both the jazz band and a cappella concerts and get your fill of music for the whole year in one day!
EDIT 2: Still looking for things to do on July 23rd? You could catch a webinar about using Matlab to process large datasets around 2 PM before heading to the afternoon/evening concerts. I know I'll be watching... or, probably not actually... but someone might find it interesting.