Got some quality information from a webinar I recently attended, sponsored by http://www.care2.com/. The topic was e-marketing, but much of the webinar focused on ways to increase your e-mail files size. Some quick data points:

• 19% of your e-mail file is lost each year due to lapsing records, email bounces, unsubscribes
• Files with accompanying e-mail addresses perform better than files with just one channel
• Bigger E-mail lists = More Money

8 ways to grow email file:

1. Collect email addresses on web site via donate or subscribe button (make very visible & very easy to do)
2. Leverage offline communications - take every opportunity to collect email address in every format
3. Encourage pass alongs (Viral Marketing, Forward to a Friend)
4. Online Advocacy - get emails from a petition people sign
5. Search Engine Optimization (SEO) & Search Engine Marketing (SEM) - Use free advertiser account through Google
6. Ask Supporters to market for you (Web 2.0)
7. List Swaps - potentially “exchange” email lists with a corporate partner
8. E-appends

Give one, or all a try. It will be worth your while.