Volunteering options in Romania usually centre on helping abandoned children or children with special needs. Organisations often have a religious or Christian undertone, and volunteers are typically expected to pay for the experience.
Volunteer Romania (www.volunteerromania.co.uk) is run by a British couple, based near Deva in Transylvania. Volunteering is done in two-week intervals throughout the year, working with orphaned or disadvantaged children.
Global Volunteers (www.globalvolunteers.org) offers one- and two-week volunteering projects helping orphans and teaching English. Volunteers pay for the experience (a two-week slot is US$2295, including lodging, food and insurance).
Sites like www.volunteerabroad.com list many other options.