What about Tad Williams' Otherland series? (Score 1)

I browsed through these comments and while several people mentioned the Tad Williams Memory, Sorrow and Thorn series, no one (that I saw) suggested his Otherland series, 4 MASSIVE volumes that could conceivably keep you going all summer. And they take place (you eventually learn) to a large degree completely INSIDE a virtual universe. This unique concept allows Williams to cleverly combine elements of fantasy within a scifi/hacker concept.

The 4 volumes are City of the Golden Shadow, River of Blue Fire, Mountain of Black Glass and Sea of Silver Light. The first one was reviewed on /. here: http://slashdot.org/books/980803/087207.shtml