It is always best to think about what he will enjoy, however here are some things I enjoy.
I will never stop raving about the
$1. It is an awesome tactile timepiece that I use every day.
You may also want to look into adapted living things. Adapted kitchen equipment (microwave, measuring implements, etc.) can be great. You can find this stuff at Maxiaids and a few other disability related distributors.
I also really like my Trekker Breeze which is a mobility GPS that has really made navigating a lot easier. These are just a few ideas, it really depends on what your dad likes.