Over the last 6 months I've seen some pretty cool results for charities and non-profits using Twitter.
Non-Profit Success Stories with Twitter

Tweetsgiving.org – Epic Change + Kbuzz
This was a very clever, well planned, successful viral fundraiser. The goal was to raise $10,000 to build a classroom for children in Tanzania.
Tactics:
Results:

One Day For Human Rights – Anca Foster
This campaign was focused on the Dec 10, 2008 Human Rights Day, and modeled after Blog Action Day. The goal was to get signatures for a petition to get the Universal Declaration of Human Rights into people's passports.
Tactics:
Results:

This is a fairly new, ongoing year-long effort for 12 different charities. Each month, a new charity.
Tactics are fluid, but they include:
And they just did a tweet-a-thon… March 19 2009 to Raise $12,000 for the Share Our Strength charity.
Results:
Real World Results
Um wow.
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