Give appropriate credit to volunteers. Show appreciation in many ways. Personal notes, recognition at events, kind words of appreciation in newsletters, etc., go a long way and mean a lot. Include a small budget line item for entertainment and volunteer appreciation. Seek diversity in your volunteer base.
Differences yield interesting and exciting dynamics and greatly enhance creativity.
Keep volunteers informed on a regular basis. Help develop new relationships between volunteers. Make it fun. Volunteers will give more freely of their precious time and resources if they can have some fun at the same time.