Egan's stuff divides evenly into near-future and distant future science fiction; the distant future stuff tends to be very abstract. His latest novel, Zendegi, is a very near-future setting, and coincidentally is a more accessible read than most of his other stuff. I'd recommend it to start with.
Egan's two most recent books, Incandesence and The Clockwork Rocket, are great if you're a math and physics guy.
If you're a programmer, Permutation City would be my recommendation. If you're more mathematically inclined, Diaspora is a good choice. Just so you know what kind of book you'd be in for, the first chapter of Diaspora has a proof outline of the Gauss-Bonnet theorem. His short story The Planck Dive gives a good flavor of Diaspora: http://gregegan.customer.netspace.net.au/PLANCK/Complete/Pla...