List of markets. What are some niches to reach out to?

So far I've only come across the obvious ones:

• restaurants
• shops
• gyms
• private trainers
• dentists
• vets
• lawyers
• health practitioners
• plumbers
• electricians
• manufacturers - materials, tools, electronics

I bet there's a bunch of better niche markets out there that are completely in my blind spot. What am I missing?

from List of markets. What are some niches to reach out to?