I have unlimited time to give

1. You can find some great options locally at VolunteerMatch. But this site also has a search function for "virtual opportunities" which you'll see if you click on the tab next to the Local one. So if you live in the middle of nowhere and have nothing but time, this gives you the opportunity to give.

2. Do you like to read? If so, you may have heard of Project Gutenberg which produces free ebooks. This all happens with the efforts of volunteers. You can help them by doing some proofreading through their partner site called Distributed Proofreaders. There are many different ways to help and at many levels.