It's impossible to have a discussion about IDM without mentioning the genre's granddaddies, Autechre. Both hugely popular and critically acclaimed, they have grown more and more experimental since their 1991 debut single. Personally, I think they completely lost the plot around 1998. That said, what they did from '93-97 is genius.
This is "Bike" from their first album Incunabula. They did better stuff later, but this is a very good introduction to the Ae sound. It's simultaneously sparse and lush, melodic and somewhat dissonant, and possessing a song structure similar to drum n bass(!)