The first one that springs to mind is The Case of the Toxic Spell Dump by Harry Turtledove. I'd been told for years that Turtledove wrote really good stuff, but, honestly, historical, alternate universe stories have never been at the top of my favorite list. I found this one day browsing a used bookstore, and decided to give it a try. It was a good choice. The story is set in a world much like our own, except magic works instead of much of the technology we use today, and there are waste sites for spent magic, much like our toxic waste dumps. When there seems to be a leak at one of these dumps, Environmental Perfection Agency agent David Reynolds is sent to investigate. From there, the plot, well, thickens.
It's a fun read, to be sure. There are jokes and puns a-plenty, but there is more to the story than just humor. Turtledove creates a world that is at once fantastical and believable. The characters are interesting, with personalities that are not just cut-out comedians. There is obviously a fair knowledge of several religions and their traditions, as well as good use of fantasy magic.
I enjoyed this one so much, I've since read several more of Turtledove's books, and have liked most of them.