reative steamed drinks and living-room ambience are the secrets of the Berkeley Perk Café, with soft couches and expansive wooden booths in front of big windows and just off the beaten path across the Berkeley Street bridge from the Back Bay. The signature beverage: the frothy vanilla chai, perfectly spiced with a sweet undertone and served in a giant mug. Need more caffeine? The freshly brewed coffee is guaranteed to wake you up. There are several varieties of hot chocolate and reasonably priced, sophisticated sandwiches, from veggie with hummus to prosciutto with mozzarella. Canal