I don't have enough nice things to say about Purple Penguin. We try to go in the middle of the week so the wait isn't as long but even when there is a line - it's totally worth it.
My favorite is the blue bubble gum. Oh wait... cherry and watermelon... nope... green apple?
Heck, I like them all and have been bugging my daughter to try the pickle juice but she's not been brave enough yet.
The service is always super friendly and this season they have umbrellas for people to use to shade themselves while waiting in the sun.
I will reiterate what others have mentioned... BRING CASH.