Keep in mind your expertise on what you plan to do. Almost anyone can paint, and there is probably a room or some trim that your mom would love to have "freshened" up. Of course, don't rush out and buy the paint of your color choice. Mom probably has her own ideas.
Bring the subject up in a casual conversation. Even a little chiding of, "If I was you Mom, I'd paint this room yellow." If Mom doesn't like yellow, she will most certainly tell you. Once you have her color ideas, you can purchase the paint, put a big bow on it, and then set a day that you will be over to paint the room for her.
If painting is not to your liking, pay attention to some of the other things Mom says. Perhaps she has mentioned she'd like to replace the porch railing, or put up shutters. There are many things homeowners would like to "eventually" do. Don't think in terms of general upkeep, but perhaps "upgrade."
If Mom enjoys sitting in her yard, consider surprising her with a new rock garden, bird bath or even a pond or water fountain. Again, use a tactful conversation to find out where she would put a pond, bird bath or fountain, if she had one. If you want to make it a big surprise, you'll need to enlist the aid of a friend or family member.
Get someone to arrange to take Mom out for lunch and shopping for an afternoon. Make sure you have everything you need to install the pond, fountain, or rock garden, in advance of the outing. Having to run get something you've forgotten can mess up your timing and your surprise.
http://www.youtube.com/watch?v=36O4fjpSDa4
Once Mom is safely squired away, get over to her house and get busy! If you are prepared and have looked at how everything is installed, you can easily do any of these outdoor projects in an afternoon. Most DIY stores such as Lowes or Home Depot will have everything you need, and their employees will even advise you on how to do it.
Your Mother will appreciate the thoughtfulness you put into a DIY gift, and she will be able to enjoy it for many years to come. These are but just a few ideas for Mother's Day that any mother would love. Look around your Mom's house; I'm sure you can find many more.
