+1 on Neuromancer which is fantastic. If you like your SF nearly possibly not completely beyond the realms of what might (or might not) feasible at some stage in the future, then Red Mars (and sequels) are worth a read.
Slightly off the wall, but a hugely entertaining read is Vurt by Jeff Noon. It's nearly my "if you could only read one SF book" choice.
Finally, Stand on Zanzibar by John Brunner is an all time classic. Look it up on google and see if it takes your attention. If it does, then grab a copy - you won't regret it.
Oh, I also have a soft spot for Otherland by Tad Williams, but I met the author once and he was a genuinely nice chap, so I may be biased!