ImprovLA is a popular, low-cost workshop on long form improvisation taught by veteran improviser and comedian Keith Saltojanes, based in Los Angeles.
From the ImprovLA website:
ImprovLA is a place for improvisers, actors, and non-actors to come together to learn and strengthen their skills as a performer and improviser. Each workshop focuses on learning the skills of long form improvisation. Whether you have no prior experience in improv or just want to workout your craft, and everywhere in between, ImprovLA can help you. In each class you will be guided through exercises to enhance your acting, creativity, listening, characters, staying in-the-moment, confidence, scenework, and overall performance.
Each class is meant to make the performer feel confident onstage and off. Taught by veteran improvisers and actors, ImprovLA has taken the bare-essentials of all of their experience and training in both improvisation and acting and created a workshop that can be the most beneficial for everyone involved.The workshop is designed as a drop-in class, meaning it has no linear curriculum; you can show up any week and jump right in. Each class focuses on a different skill to make you better, smarter, stronger, and more confident at improvising.
He also hosts a weekly podcast by the same same.