Chillies have the closest requirements to Cannabis - you could grow them at the same time. You won't introduce any bugs if you grow them from seed, and maintain good hygeine. Don't take any plants out of the garden though.

Otherwise, in no particular order:
Under HPS:
Bell peppers
Cherry Tomatoes
Physalis (Cape Gooseberry)
Basil
Aubergine
Ornamental Cutting Flowers (Especially miniature rose, lily, carnation)
Citrus trees.
Geranium (Pelargonium)
Marigold
Under M/H
Blueberries (Require acid soil)
Parsley
Cucumber (Might get a bit large)
Lavender
Coriander
Under CFL
Orchids
African Violet
Spinach
Lettuce (Under 21 degrees)
Basically go for expensive flowering or fruiting plants. Root vegetables, brassicas and winter veg are all out.