During National Mentoring Month, don't just thank your mentors. Give them the resources to build lasting relationships with their mentees. You might start by handing them the Search Institute's checklist for mentors (PDF, 193KB) to help them plan fun new experiences. You can also send them to MENTOR's Resource and Publication Search, where they'll find more ideas for activities, training manuals, guides to help them navigate every stage of a mentoring relationship, and advice about working with mentees of various backgrounds.
To hear one perspective on how programs can support volunteer mentors, read NCFY's recent article "One Mentor's Take."