Full disclosure: I've been reading Infinite Jest in fits and starts since 2007, and I'm still only halfway through it. I've used it for inspirational "bible dips" (I don't own an actual christian bible) or just plain inspiration for writing. Recently, I watched The End of The Tour, based on David Lipsky's book-slash-extended interview with Wallace, Although Of Course You End Up Becoming Yourself, both of which I highly recommend.
Here's Jason Segal on how it was to play Wallace in the movie.
I wish I could recommend Infinite Jest itself, I just don't know to whom. For DRW, I'd go smaller: Girl With Curious Hair, the excellent and oddly, Oblivion, his last collection of short stories. I've always preferred Wallace as a short story writer, though that says more about my attention span than it does his skill as a novelist. Or even his essays, which get kind of overlooked.
Either way, happy birthday to generational-defining hunk of a novel.