This book has been around for a while but is always wise and comforting.
Here's an excerpt:
Whenever you can, offer the gift of your time. People who feel lonely and disconnected often think that no one cares about them. Instead of plopping down on the couch to watch TV for a few hours each night after work, why not pick up the phone and call someone you know who struggles with loneliness? Or, better yet, get together with her in person. The gift of time is a precious commodity nowadays. If you can take even an hour here or there to devote to one who needs support, you'll be performing an act of great kindness. There's nothing more uplifting to someone who struggles than to see a friend walk through her door ready to listen.