Another vote for "Otherland". Stonking series. I found the ending a bit weak though (the "Memory, Sorrow and Thorn" series had a similar problem). I've also got Tad Williams' other books "Caliban's Hour" (a retelling of "The Tempest" from Caliban's POV) and "War of the Flowers". "War of the Flowers" is just stunning - most of it is very funny, so the few moments of outright horror in it are even more shocking. Which I guess is the point. For my money, Tad Williams is one of the best writers anywhere - the only thing he's missing is slightly tighter control over his plots, but the writing itself is amazing.
Kim Stanley Robinson's "Red Mars" didn't impress me, so I don't plan on ploughing through the other two just for the sake of it. Rather like Arthur C Clarke, it seemed like he had some great "hard sci-fi" ideas but wasn't a good enough writer to turn them into a decent book.
Most recent acquisitions are a few books on luthery, which have showed me how unlikely it is that I'll ever build a musical instrument from scratch myself! :-(
Otherwise it's all been re-reading stuff like Pratchett recently. Got to find something new to read...