The "charging completed" notification sound can be pretty annoying, especially when it comes on at 3am. Here is a solution (requires rooted device):

1. Download silent.ogg
2. Rename it to TW_Battery_caution.ogg
3. Copy the file to your phone
4. Move it to /system/media/audio/ui overwriting the existing file. You can use Root Explorer for moving, and don’t forget to back up the original file!