So I'm on a Neil Gaiman kick right now. The first Gaiman work I came in contact with was the picture book There Are Wolves in the Walls which was illustrated by the same artist who did Sandman with him. Wolves is a very interesting post-modern picture book, kind of dark and creepy.
Next I read Stardust, which is a Victorian-style fairytale adventure. I found it in the YA section of the library, but it read like mainstream. For the most part I liked it--it felt reminiscient of the Andrew Lang fairytales, but influenced by modern writing style. Caution: there are a couple of short sex scenes.
I just finished Neverwhere, mainstream fantasy that takes place in an alternate world in the London underground. I enjoyed this more than Stardust, but that could partly be because it took place in London, and since I did study abroad there I am desperately in love with London. Reading about all the familiar London sites made my heart ache for this favorite city of mine. But it also made the book more enjoyable--I knew just what Gaiman was talking about when he would mention Leicester Square, the National Gallery, the walkway along the Thames, etc. I definitely recommend it, just for its imaginative prowess. Gaiman has such an interesting, darkly fantastic world here. Caution: not for the faint of heart, plenty of violence and blood.
My next read is Good Omens which he wrote with Terry Pratchett. EUOL highly recommended it, so I think it will be good. Gaiman seems to have a flair for darker fantasy, twisted slightly, but with positive themes; I'll be interested in what else he writes.