I have been a SAHM for most of my kids' lives. It was a mutual decision. However, I find there are more than plenty outlets to be productive and creative.
Some others already mentioned various ideas for working from home, for example marketing something (cosmetics, cooking utensils, toys, books, etc) While you would be able to work from home, it will require support from your husband, as some of the meetings and events are likely to occur in the evenings or weekends as well. I sold Discovery Toys for several years, and loved it, as it got me out of the house and in contact with others. I loved the products, and the best part was that we had so many of the products at home, as I had them as samples to show and demonstrate. We got to play with the toys, test the games, read the books - my kids loved that UPS guy! LOL
And what a great source for good quality presents (at a huge discount from retail) for all those birthday parties my kids got invited to, and for teacher's gifts, etc.
Doing that kind of work you do have a great amount of flexibility, but it also requires a good dose of self-discipline and occasionally you will need to schedule an event in the evening or on a weekend if that is what works best for your customer.
Data entry and such that you can do from home may interfere less with the home life, but I don't know that for sure, I have not done that.
I am lucky in that my husband's income does provide us with all the necessities. We do live frugally and are careful where we spend our money, but it works, and I enjoy being able to be home for my kids (who are now middle school and high school), and they know that they are lucky and do appreciate to have me at home when they get home, that I am available to pick them up after any after-school activities which prevent them for taking the bus home, and also that I am 'there' if something happened in school they need to share when coming home, or if they need help with some work, studying or a project.
However, my day does not revolve only around my kids and household. I joke that I am a professional volunteer, as that is what it often feels like; I probably volunteer as many hours each week as I would spend working a full time job. But in the pockets of time that I have available, on my own schedule (mostly).
There are so many non-profits, organizations, clubs, schools, churches and shelters that are desperately looking for volunteers. What is your passion? What do you feel strongly about? What skills do you have to offer? You couold go and be actively involved with some hands-on activities (tutoring, reading with kids, class room helper, sorting throg donations, picking up or distibuting donations, walking dogs at the animal shelter, helping with fundraising activities, etc). Some work you could do mostly from home: stuffing envelopes for a mailing, data entry, putting together their newsletter, writing for them, answering inquiries, etc.
Are you crafty or creative? Consider knitting or crocheting caps, blankets, mittens, sweaters, etc either for donation to your local shelter or hospital (check what they most need); or find a store where they might be happy to sell them for you. Maybe you have a knack for making jewelry, beading, scrapbooking, greeting cards, soap making, flower arranging, ...?
Some of these crafts and items could be sold via ebay as well, if you can't find a fairly local store to sell them for you.
Do you like cooking and/or baking? basket making? gardening?
I am sure, if you do some soul searching and think about what you REALLY like to do, what you have an interest in and a passion for you will come up with something. And then think about what you can do with it and how to approach it, be it as a volunteer, for raising funds for a non-profit, or to actually provide you with some income.
Yes, and then there is going back to school (on-line is always an option), getting a degree, or also apprenticing with a crafts(wo)man, maybe you have someone fairly close who does a great job restoring antiques? upholstering furniture? painting furniture? making pottery?
I hope I have offered you enough suggestions to spark your own ideas and imagination, and I wish you that you will find something to fill that void you are feeling, to become once more productive and creative in some way of the myriad ones out there.
Best wishes!