Well, I repeat myself, but The Black Flower, and The Year of Jubilo, both by Howard Bahr, are definitely can't-put-down. Admittedly I am biased because the author is a personal friend, but I hadn't met him at the time I first read his books.

Another one I couldn't put down, was The Woman in White by Wilkie Collins. This was first published in the 1860s, and is a fantastic mystery with so many twists and turns, your head will spin. The prose is extremely slow, because it's Heavy Victorian, but I had to keep reading, because I had to know what happened next! Well worth the trouble.

I am also a huge Louis L'Amour fan. I love his books striotly for entertainment value. These are great waiting-room reads because they move along quickly, and are usually pretty short.

A short novel I read recently is Catherwood by Marly Youmans. It is officially out of print, but used copies can be found easily on amazon.com.

Someone may have already mentioned this, but Zane Grey's Riders of the Purple Sage is pretty exciting too.

And... I have read many of the books on Gargoyle's list, and have to agree. Victor Hugo is one of my favorites, and everything I've read by him has been a not-put-downer.