Won't join all of them, but these look interesting

Research

• The U of T Human Factors Interest Group
• Knowledge Media Design Society (eventually)

Business

• U of T Entrepreneurs' Club (UTEC)
• Asia-Pacific Student Entrepreneurship Society (ASES)

Outreach

• U of T Local Actions Impacting Globally (LAIG)
• U of T Junior Undiscovered Math Prodigies Tutoring Chapter
• U of T Best Buddies (St. George Campus Chapter)

Misc

• Students for the Advancement of Women (SAW)
• U of T Women in Science & Engineering (WISE)