On the fiction side of things, I'm planning to start Heinlein's Stranger in a Strange Land soon. It seems like a good choice given how much I liked The Moon Is a Harsh Mistress last year.
In the non-fiction, sports category, the next two up are Forever's Team and The Secret Game.
In the non-fiction, not-sports category, I'm going to finish the second half of The Problem of Political Authority by philosopher Michael Huemer. I set it down for a while because I had other priorities and am already familiar with the content, but it's very good. I find that philosophers tend to write with one of two styles: either careful, precise arguments or gobbledygook faux-esoteric language obscuring a lack of actual substance. This book uses the former and I'd recommend it to anyone who has an interest in political philosophy.