1. Find seminal and survey papers from their fields that are unavailable on Google/Citeseer/etc, whose authors are dead/moved on/unfazed by the Internet/etc.
2. Download digital versions of these papers through their institutional access, or scan in paper copies if necessary.
3. Post them on their personal website with appropriate titling (especially important for papers that have been through scanning) such that they will show up in search engines.
It's also a minor way to have some influence on what gets read and cited. A lot of academics have a favorite classic paper they feel is unjustly underappreciated in their field. Why not put it online? Getting the paper into Citeseer and Google Scholar, where someone might stumble across it, is a small way to help promote underappreciated work. An underappreciated paper nobody can find is going to stay underappreciated!