I will pretty much read anything.
Actually, I try to be selective within genres–for example I read Bridget Jones' Diary, one of the most influential and earlier "chicklit" books, but I haven't read widely within the chicklit genre. But, more generally speaking, I will pick up pretty much anything.
I devoured all the Star Trek novels in the Swasey library as a kid and even continued to read them through high school and even into college. I've read pot-boilers like Clive Cussler and Dan Brown. I've read a bunch of old classics–Dickens, Verne, Hugo (helpful hint: reading old French books is easier than reading old English books, because the translation puts it into more modern English. The Phantom of the Opera and Les Miserables are easier reads than say, David Copperfield, although I like that book a lot too.) I've read mysteries (of course). Fantasy (and many of the sub-genres with fantasy). Biographies, high modern literature, historical fiction, obscure sub-genres of genres. Etc.
Sometimes I discover new genres and books by asking simply "What's your favorite book?" and then going to read that book.
For a lot of guys, the answer has been war novels, adventures, and a lot of books I likely would have found anyway. But when I've asked women, I've found books I never would have read before. Childrens' books like Anne of Green Gables. Post-Apocalyptic feminist literature (yes, that's a genre) like The Gate to Women's Country. Historical romance novels like Outlander. The absolutely freaky and disturbing S&M novel The Story of O. (Yes, I read it. Yes, it was someone's favorite book. No, I had no idea what it was about when I borrowed it from her. No, I still cannot believe she actually referred the book to me and actually loaned it to me–I feel embarrassed enough just admitting I've read it.)
I think it goes without saying that reading widely has been incredibly helpful to my writing.
My favorite snippet from a review of The Marinara Murders came from the blog of a very well-read high school senior.
Those threaded stories – those interlocked personalities – were probably my favorite part of the book. Unlike your basic modern mystery, there were no pure stock characters involved. Each one had its own complete identity. The cop was harsh, but friendly. The lady threw a killer punch and played hockey. The wayward teen activist scrambled around Europe, but came to have a keen business mind as well. No one was just their basic title.
(FYI. This is exactly what writers want to hear in a review.)
If I have been successful in this (and I'm not saying I have, because it's by far one of the hardest things for a writer to pull off), it's because I've read widely, and read books with characters that would never appear in "your basic modern mystery."
And if you've read this far, here's something that's exciting to reward you for your loyal reading: this past week I finished the first draft of a new Arthur Beautyman short story!
What does that have to do with reading a wide variety of book? Well, in this particular case, the fact that I have read a few romance novels probably came in handy! No, Beautyman doesn't find love in this book. But I think the short story turned out really well, and I'm excited to launch it.
Of course, all this makes it sound like I read for the sole purpose of being a better writer. I do it because I love reading interesting books, especially books that will surprise me. And to read books that will surprise me, I like going outside the same set genres to read new things with new conventions, and new characters.