T.
My daughter and I have made plates and mugs with handprints and footprints (infants can't usually do handprints) at the painted pottery places. You would have just enough time to get it back fired and glazed if you did one now. It's little more permanent then plaster of paris (unfortunately, also a bit more expensive). On the back/bottom we write messages of love and the date. We got the idea from a friends husband who made a beautiful plate with their daughter's handprints and his with a boldly written "We love you!" emblazened across the front with a heart. I've always wanted to do this with my nephews and my daughter on one plate for grandma.
Other ideas my mom has loved are certificates etc. for things she doesn't like to do. She hates to garden, but my SIL and I enjoy it -- so we bought her some beautiful perenials and planted them for her. We've actually done this a few times -- she has a wonderful garden now which she enjoyes even more because she didn't have to do any of the digging! Hanging baskets for outside are a nice alternative -- they will brighten an outdoor corner all summer.