You say, "Whats a good pet for a busy 10 year old??" If he is that busy does HE really want the pet? Like others have said any pet requires care and time. If your child REALLY wants a pet they will find the time to care for it, otherwise it will be your pet!
With that said, I have a 10 yr old daughter and she loves animals. I started small and built up because it was "her pet" and not mine (I have our dog! and don't want or need to care for another animal!). We started with fish and hermit crabs. SHe learned to clean the cage/bowl monthly and feed as necessary. Only once she mastered that did we consider buying her a gerbil/hamster. You can clean their cage every 2-4 weeks. Water bottle and food hold alot so it doesn't have to be done daily. She waits many times until the the cage smells bad to clean it (it is in her room so I really don't care). She now wants a rabbit but that's a big leap.
Growing up I had a parakeet. They are a bit messy... when they fly around the cage their feathers and food get all over. However, the cage is easier to clean then the gerils and less smelly (I think)! Food and water can stay for a good amount of time like the gerbils so it is not a daily thing.
Bottom line... give your son some choices that you feel comfotable with and see where his interest lies. If he really wants the pet, you need to explain that it is his to take care of. I would really suggest you test the water with other animals (hermit crab, fish) to make sure he will care for the new pet. Too many kids think it is so cool to have a pet, but do not realize the commitment. And, I would suggest not interferring ... let him care for his pet --- reminders might be necessary but don't do the work. If there is a place in your child's room for the animal, I think that helps for them to take ownership of it.
Reasearch animals online --- maybe snakes might be easier?