What are ongoing charities (Sadaqa Jariyah)? Do Islamic tapes count as one of them? And does the reward reach those for whom I intended the charity when I donate a small amount on my behalf and on theirs?

It is permissible to dedicate tapes (audio or video recordings) as an endowment for beneficial use, and it is considered an ongoing charity (Sadaqah (definition) Jariyah) for which a person is rewarded as long as it remains. It is also permissible to share in the charity, by intending to include others in its reward, and everyone will receive the reward. The book "Al-Iqna'" from the Hanbali school mentions that every act of worship performed by a Muslim, the reward for which, or a portion thereof, is dedicated to a living or deceased Muslim, is permissible and benefits them.