I'm going to give a few titles and authors that fuse elements of sci-fi and fantasy... and aren't as widely read as they should be.

China Mieville:
1. The Scar (not his first book set in his world, but it is certainly his best book) A steampunk style novel set on a floating city of pirates. There is a fair amount of intrigue, suspense, action, and just plain awesome.

2. Perdido Street Station A very good book, that mixes equal parts action and horror. This book features some of the greatest scenes that I've ever read.

Tobias Buckell:
1. Crystal Rain (The first book in his loosely connected series) The book is difficult to describe. It features a Caribbean feel with a strong, almost classic, Sci-Fi story.

2. Raggamuffin (The second book) This novel follows from the first novel, but is more firmly sci-fi and has a broader scope.

3. Sly Mongoose (The third) This novel is just simply awesome. It's a good sci-fi/steampunk adventure and suspense story. It also features space zombies and an awesome protagonist.

Neal Stephenson:
1. Snow Crash Probably the closest thematically to the Otherland series. It is the novel that first made a name for Stephenson, though it differs greatly from his later works. Besides, I love it for the Deliverator.

2. Cryptonomicon This is just simply a great novel. There are three primary threads that weave together to create a single story... one that takes place both during WWII and during the 'present'. The story is part adventure, part mystery, part war story... and all awesome.

3. Anathem This just might be my favorite novel on this list. It's not perfect, but Stephenson nails his storytelling here. The way his scope and focus gets bigger and bigger, the story and the stakes getting larger and larger... just a truly great read.