I'm going to check out some samples first to remember what their sound is like.
As for
Meat Beat Manifesto, I'm not saying they are alike, but they come from similar backgrounds and influences. I only brought them up because of your description, "...avante-garde, left-of-centre (or just IDM if that's how you wanna look at things) place. They have a sample-heavy sound which incorporates dub, hip-hop, ambient, down-tempo, even psychedelia and jazz...". I'm thinking that FSOL is probably a bit more on the trancey/spacey side of things, but they both fit that description.
I enjoy much of MBM's work but would recommend
Armed Audio Warfare for a real aural assault (think industrial dance hip-hop?), and
Satyricon for something a bit more groovy and laid back. Those two should give you a good sense of their early sound.
99% should be considered too. They all may sound a bit dated, but I'm sure FSOL do too, at least in the production. The latest MBM from 08 is actually really good too, with a big dubstep influence. Though I always say that MBM has always had dub undertones...and that today's dubstep artists were probably influenced by MBM whether they know it or not.
