I take digital photographs of nature stuff. There has been a lot of interest in buying them but i really haven't pursued it as much as I should.
People pay big money for dog watching around here. If you are working you probably couldn't do daycare but you could do weekend boarding/babysitting. My school had a local fundraising auction and I donated a weekend of dogsitting. Someone paid the school $200 for that!! Depending on the level of service you offer (are they staying at your house all weekend, or are you just going over to feed, let out) then I would charge $50-$100.
You could also offer to do night and weekend babysitting as long as the children were old enough to be left alone while you use the bathroom.
I also agree with crocheting. Scarves and blankets are easy to make. In my area there are co-op stores where people can bring their craftss to sell. Also the famers markets allow you to rent a table for cheap. Flea markets would probably work too.
The easiest and quickest thing to sell on ebay or half.com or amazon is books. You can sell old text books for a lot if they are still being used at other schools. I sold all my old babysitters club books and sweet valley high stuff. Half.com will tell you what the new price is and what others selling the same book used are charging and then you can adjust your price accordingly.