My boys are on a roll with coloring pages, much to my continued shock and amazement. I don't think they are necessary for homeschooling but if they want to do them while they listen to me read aloud, that is fine with me. They beg to be able to color with their Prismacolor colored pencils while I am reading aloud. We are learning about forest creatures right now and are using the Dover Coloring Book: Small Animals of North America by Elizabeth A. McClelland. These are high quality, detailed images which are even suitable for adults to color in.
I also have used some free coloring pages from www.enchantedlearning.com. I have not yet been able to justify the $20 annual membership fee which allows access to larger sized images due to our very tight budget, so I am settling for the smaller free images. I figured out that I could copy the information from the site and paste inside of my word processing software, I can then delete some or all of the text, leaving the image, then printing that on my computer printer. I would prefer the image to be full page sized, but this is what I have to settle for, for free.
For history, we continue to use coloring pages from within the Story of the World Volume One Activity book and also use some of the history themed Dover coloring books.
I keep a three-ring binder for each subject for each of my children. Their colored images, original artwork and narrations are kept in these notebooks as well. I'd add photos to these notebooks as well if I ever get to print the digital images which for now are stored on CDs!