I want my partner to take my children and myself to a local park and take snapshots of us playing, not necessarily posed. I generally manage to snap some Daddy shots as well. This works out to a TIME / EVENT gift with digital outcome. It takes up NO space in the real world. It is a gift of attention and I am nothing if not an attention whore. (You don't have to be one to enjoy this gift, though!) The other great thing about this gift? It is FREE!
Alternatively, I also recommend Zoo or Museum Membership. It is something else a mother can enjoy sharing with her family and it doesn't take up much in the way of real world space.
Whatever you receive or do for Mother's Day, have a wonderful one! Remember: it is YOUR day!