Have you considered Todo.txt Touch? (While it's $2 in the Market, if you don't care about getting automated updates, you can download it for free from the author's site.)
It expands on the simple philosophy of Todo.txt where your to-do list should just be a simple text file.
While you'll need to use Dropbox and share the file, once it's set up you don't really need to touch it except on your phones.
Here's how you'd set it up (assuming you and your wife share a computer):
- Set up your todo.txt in a todo directory in Dropbox (basic Dropbox is free and is a great tool)
- Install Todo.txt Touch on your phone and give it your Dropbox credentials
- Repeat step 2 for your wife's phone
- Now you have a shared, as-powerful-or-as-simple-as-you-need To-Do resource
Here's how you'd set it up (if you and your wife don't share a computer):
- Set up your todo.txt in a todo directory in Dropbox
- Share your todo directory with your wife's Dropbox account
- Install Todo.txt Touch on your respective phones, using your own Dropbox credentials
- Now you have a shared, as-powerful-or-as-simple-as-you-need To-Do resource
It seems like it might be a lot of work, but it's not. Further, you only need a simple text editor to work with your todo.txt file while at home.