Project OUT: provides education, support, and financial assistance to Trans people
Venture Out Project: Group hiking, backpacking, skiing, and other outdoor trips, by and for LGBTQ+ people. Has Trans-specific trips, youth-specific trips, and a family camping weekend for younger kids.
Youth On Fire (YOF): for homeless and street-involved youth aged 14-24. Located in Cambridge, MA.
Outside New England
Gender Spectrum: helps to create gender-sensitive and inclusive environments for all children and teens. Support, resources, info, and trainings for families, schools, etc.
Trans Lifeline: Crisis hotline in the US and Canada staffed entirely by Trans people. Also offers microgrants to help you change your name or gender marker.
TransBucket.com (surgery results - big database, great info and pics - NSFW)