April is, among other things, Autism Awareness Month, so you may see tables for autism advocacy organizations around (especially on college campuses).
Do not donate to Autism Speaks- they have no autistic people on their board, have refused to hire parents with autistic children, use legal threats to shut down criticism of their organization from people with autism, adheres to the widely-discredited theory that vaccination causes autism (in that they dump money into researching the connection), and are generally not useful or well-liked by actual autistic people.
Generally, the endeavor is like Susan G. Koemen, a big fundraising loop (they sell products to ‘raise awareness’ and then use those proceeds to sell more products) that fails to benefit anyone but those pulling salaries from the effort, who are notably not autistic. Only 4% of their budget goes to services for autistic people and their families.
Instead, donate to the Autistic Self Advocacy Network, through the title link.
(Thanks to greencarnations for the information.)