I think some related genres include: Downtempo, trip-hop, chillout, ambient... that's all I could think of right now.

Anyway, I like listening to (that's related to this type of music): Boards of Canada, Bonobo, Nujabes, Explosions in the Sky, Blur, Broken Social Scene, Mum, Air (not the anime), and that's all I could think of right now.
But anyhow, these types bands are somewhat slow compared to Aphex Twin.