I'm working on a custom "Do Not Respond" list. I initially started building it as just a text list, but decided that's a stupid way to go about it. If you have two people listed in your contact list with the same name (Which, amazingly I do have at lease 1 set of contacts with the same first AND last name) it would block them both, since it is blocking by name.
So I decided to try to implement a contact selector instead. This idea should block based on contact number, which is a number unique to each contact in your address book, instead of by name. I haven't implemented the actual contact selector yet, but looking at some sample code, it doesn't look to be too outrageously difficult. It may take some time though.
Here is a preview of what the "Do Not Respond" list will look like. If the contact has a picture associated with it, it will display that picture instead of the generic contact picture.
I may keep the blocking by name in as well, but I'll have to think about how to implement both of them at once. (I'm sure it won't be too hard, I just have to take the time to do it.)