Wow! What an awesome list! My favorite is the stock photography because I love photography. I have had some success there, particularly with one photo I make some decent income from. I think the key with stock photography is finding a shot that is high demand. Then, find a new unique way to frame that shot. This is the reason my St. Louis Arch photo is a top 10 on both ShutterStock and iStockPhoto. Thanks for the awesome ideas above!
If you're looking to get started in real estate, look at a crowd funding solution like RealtyMogul. It works similar to LendingClub - you commit as little as $5,000 towards a property. When the property is fully funded, you become an owner, and will receive your share of the earnings and appreciation in the property. Check out RealtyMogul to learn more.
In addition, you must know how much you want to earn by joining affiliate programs. Will it be your main source of income or just an additional one? For the first scenario, you should consider promoting products that are expensive and, consequently, that can bring you a good profit. If you plan on the second scenario, you can opt for affiliate programs that pay for sign ups or affiliate programs that pay daily.