Got mine off Amazon.com, as everyone else seems to be recommending. Nice and cheap.
Also, it might be off-topic, but I hope that if Indy IV ever does get made, LucasArts will start lavishing the same amount of attention to the Indy EU that they do to Star Wars. Better books, better games, the whole kit and kaboodle. I can't help noticing that despite the general fun of the Indy novels, the Star Wars books tend to be slightly higher quality. Maybe George could convince a couple of writers to switch trains.