What are /r/BabySignLanguage's favorite Products & Services?

From 3.5 billion Reddit comments

I use this book (it’s ASL) and it is great!! Baby Sign Language Made Easy: 101 Signs to Start Communicating with Your Child Now https://www.amazon.com/dp/1641520779/ref=cm_sw_r_cp_api_glt_fabc_34PKNZ3ZFXCRJ1NEKMR4