Note: You will likely see Gandhi named as "Mahatma" instead of "Mohandas" in some of the readings. It's a special title he earned later on in life. It means "Great Soul" in Sanskrit language.
BBC iWonder: Gandhi (Excellent overview and timeline!)
Biography.com: Mohandas Gandhi
Britannica School: Mahatma Gandhi
Constitutional Rights Foundation: Gandhi and Civil Disobedience
Crash Course History VIDEO: Nonviolence Movements (features Gandhi)
NewsELA World Leaders: Mohandas "Mahatma" Gandhi
Stanford MLK Institute: Gandhi (and how he influenced MLK)
United for Human Rights: Mahatma Gandhi
Crash Course History VIDEO: Decolonization & Nationalism Triumphant
Crash Course History VIDEO: Nonviolence Movements (features Gandhi)
Eyewitness to History: Gandhi's Assassination
Google Arts & Culture: Mahatma Gandhi Resources (lots to choose from!)