I'd like to first note that money isn't my driving force for any of this. It's been on the back of my mind since I started in 2 very different industries.
I started a motorcycle community in 2009 that has taken off and typically we have meets with about 30 people every Saturday and Sunday. It's grown nicely and my goal has never been to profit from it. In fact I've invested quite a bit of my own money into it without asking for a return. T-shirts are a great way for me to profit, help the community grow and raise money for charities.
Starting 2 weeks ago selling t-shirts, I was able to sell 72 total. I'll relaunch this campaign with a slightly different design in 3 months.
2. Video Games
My gaming communities are quite massive, with over 300,000 fans of my own. The community isn't as tight as the motorcycle community, but it is definitely there. I've profited off of this industry quite heavily with sales of video games, game consoles and advertising for companies.
Last night I started a new campaign trying to sell t-shirts which has already sold 12. That's a pretty big achievement in my opinion as video game and console sales usually sold about 5 in a day (but sold consistently) the fact that I was able to sell 12 without heavily promoting it is exciting to me.
Anyways, there are my case studies, Take them as you may but understand that communities hold a lot of value. I've done a lot more with vinyl stickers, custom equipment and other techniques as well.