The Church of Jesus Christ of Latter-day Saints has over 5,000 service missionaries (another site said 3,000) that work without pay to aid the poor.
(Accurate as of ~2003.)
Aside from providing service missionaries, the Church also has 61,000 proselytizing missionaries in over 300 missions in 165 countries, distinct from those mentioned above, that also work without pay. Trained in 17 missionary training centers scattered across the globe, these proselytizing missionaries provide those who are seeking God with more information about our beliefs. 93% of LDS missionaries are college-age, and 22% are female. Proselytizing missionaries are instructed to donate half a day each week doing non-proselytizing community service.