Funerary rites differ widely across cultural time and space, and customs that seem normal to their practitioners can seem bizarre and macabre to outsiders. Certain Zoroastrian sects—such as the Parsis of India—famously place their dead atop dokhmas, or "towers of silence", to be devoured by vultures. In recent years, the decimation of India’s vulture population due to diclofenac poisoning, and the construction of modern high-rise buildings which provide an unintended view of the process, make the future of this custom uncertain. (If you’re feeling morbid, you can get a vulture’s-eye view from this video.) The Tibetans sometimes practice a similar custom known as "sky burial" (warning: graphic photos).
In southern China, the ancient Bo people hung the coffins of their dead on the sides of cliffs, where they can still be seen today. Similar customs have been practiced in the Philippines and Indonesia.
Cultures from around the world have practiced endocannibalism, or eating of the dead. The Aghori of India retrieve decaying, incompletely cremated bodies from the Ganges and eat them. Several cultures—the Yanomamo of the Amazon, the Amahuaca of Peru, and some African tribes—grind up the bones of their dead, and cook the bonemeal into foods which are then consumed by members of the tribe.
Then there’s the Taiwanese practice of second burial, which involves digging up a loved one’s corpse a couple of years after burial, cleaning the bones, and relocating them to a family mausoleum.
(I’ve been researching the Parisian catacombs. There’s surprisingly little information about their specific features on the web. However, I’ve made some progress—thanks largely to Google Book Search. One of these days I’ll clean up my notes and post them here, along with links to photos.)
I’ve been in the Paris catacombs. They’re entirely badass.
I had to take a class on death and dying, so if you’re itching for some academic reads, I can hook you up with some textbooks. As the descendant of a prominent undertaker, I’d like to encourage your morbid fascination. ;-P