2006 Revenues: N.A.
Full-time employees: 600 full-time staff; nearly 4,400 corp members
Type of company: Education nonprofit
What makes it so great? This nonprofit trains new graduates who don't have any previous teaching experience and places them in troubled and low-income school districts around the country. Salaries are paid by the local school district. This year, the corps will be working in 25 school districts. Since its inception in 1990, Teach for America has had a huge impact on American education, with more than 14,000 college graduates completing the program; a study conducted by Mathematica Policy Research, a Princeton, N.J.-based social policy research firm, showed that TFA instructors are found to be more effective than the average teacher in their district. The program has been likened to a domestic Peace Corps, with long work hours and much emotional demand, so it's not for the faint of heart.