Patrick Whitefield's favourite Perennial Vegetables:

Daurbenton's Perennial Kale
Sea Beet
Herb Patience
Musk Mallow
Onions (WIld Garlic, Garlic Chives, Welsh Onions, Tree Onions, 

Fruit 
Alpine Strawberry

Self-seeders:
Lamb's Lettuce
Land Cress
Winter Purslane
Rocket
Nasturtium

Herbs:
Mint
Marjoram
Lemon Balm
Fennel
Chicory (but is it perennial? he asks, having never managed to get it live longer than a year)

Others than he gave the thumbs up during SLU course:

Jersey Walking Stick Cabbage
Walking Onion
Leaf Beet
Orich