The Milkshake Factory is within walking distance of my workplace, so I often come here with a crowd of 10+ people looking for a way to cool down. I know some establishments might be annoyed by the sudden onslaught of customers, but the staff are always really nice and surprisingly fast at serving us!
I've tried a number of the milkshake flavors here, although I usually go with regular Chocolate or Piece of Cake. Flavors that I can't personally vouch for but are popular with coworkers include Oreo Mint and Strawberry Cheesecake. They have a Cajun Chocolate flavor with a really spicy aftertaste too -- not for the faint of stomach!!
Their chocolate and candy selection is really impressive; every time I go in I marvel over all the different varieties but I've never actually tried them. One day, perhaps.
One final thing: make sure to bring cash with you unless you plan on stocking up on sweets, there's a $10 minimum for debit cards.