My favorite thing to do as a GM is bring out one of the crazy random tables that I've found on the internet or in one of my books to resolve a situation. This is most frequently done for things like damage, insanities, mutations, and similar. However, there is nothing like bringing up a random petty loot or a drug effect table. It tends to be what gets talked about for the longest.
Dark Heresy was my introduction to critical hit tables actually being used in a session. I'd read about them before, but hadn't experienced that yet. The tables sorted by weapon type and body part combined with the exploding damage produced an amazingly destructive but also extremely entertaining experience. Of course, this was really made possible by the Fate points which allowed the players to not get completely screwed over by dying.
I recently got a hold of the Warhammer Fantasy Roleplay 1st edition GM screen plus 2 booklets, one of which is just critical hits. The earlier, raw-er tables are a real joy to check out. They also provide a nice alternative or supplement to the Dungeon Crawl Classics critical hit tables.
One of the most best blog posts I've read was a short review of a bunch of books of random tables on the Gnome Stew blog. Here is a series of brief commentaries on a bunch books of random tables I've picked up over the years. There is a wide range in quality and of styles in this variety of books.
The Dungeon Dozen: This book and the accompanying blog are great sources of weird inspiration for how to randomly deal with strange situations. While I really enjoy reading these tables, I've not found them very useful at the actual table, making it a very GM's side as opposed to PC side experience.
d30 Sandbox Companion: Great tool for providing set ups or surfaces to riff off of. Big fan. Hard to use at the table.
1e Oriental Adventures: One of the coolest parts of this book is the method for generating a series of yearly and monthly events. Great fodder for a longer running sandbox like game. Impossible to use at the table.
Renegade Crowns: Another book that is impossible to use at the table. However, this book is amazing. It takes on the very odd task of providing series of random tables to completely generate a "working" brutal, grim fantasy sandbox. Complete with monsters, towns, rulers, and ruins this book has it all. Some people were disappointed that it wasn't an adventure, I've found this book unbelievably worth it. Perfect for sandboxes, point crawls, fiefdoms, and the like.
Karak Azgal: Similar to Renegade Crows, this is a "fill in the blank" style adventure. It describes two towns on the surface, a dwarven fortress and a shanty town of adventurers. Underneath is the ruins of an ancient dwarven city. The ruins are infested with all manner of beasties. The book provides almost no maps of the underground and instead provides a series of nested random encounter tables and a series of points of interest. The encounter tables include interacting factions and neutral parties. The points of interest are sources of the wandering monsters or even worse horrors. Amazing tool for a GM wanting to generate a believable series of dungeon levels.