Becoming a professional organizer is also a great way to supplement your income. You can help people with the clutter in their closets and home offices, and set your own hours.
Other ideas include blogging and freelance writing. Instead of set hours, these jobs usually have deadlines, allowing you to work on your own time.
Be aware that some of these jobs may require training or a college degree. Also, be wary of any emails you receive promoting work-from-home jobs that ask for money upfront. These are often a scam.
Along the same lines, dog grooming can be a lucrative business as well, and can be done in your own home. Some training is required, and you will have to purchase necessary supplies, but it can be a great, flexible way to earn some extra cash.