Not SciFi, but epic: Robert Jordan's Wheel of Time series -- last book (14) is due out later this year
I like The Foundation series, but if you read all of them, it's like 11 books. Asimov did a great job linking seperate but related series together:
- Caves of Steel, The Naked Sun, The Robots of Dawn
- Pebble in the sky
- Prelude to Foundatioin, Forward the Foundation
- Foundation, Foundation and Empire, Second Foundation
- Foundation's Edge, Foundation and Earth
There are also three new Foundation books by different authors that are also very good:
- Foundation's Fear (Gregory Benford)
- Foundation and Chaos (Greg Bear)
- Foundation's Triumph (David Brin)