Prehensile Tail

Wouldn't life be just super if you had a extra hand attached to your spine? One that could be used to fetch your coffee or dial your phone? Or beat the crap out of that yappy dog?

It should be noted that Petting Zoo People and Horny Devils both tend to have these for Fantastic Arousal Service. Also, Beware My Stinger Tail is when the tail has stuff attached.

Examples of Prehensile Tail include:

Anime and Manga

The Saiyan's tails in Dragon Ball, though only Goku gets the best use of it. In fact, any Dragon Ball character with a tail (or head tentacle) fits.
The Pokémon Aipom has one of these, with an actual hand on the end. Its evolved form Ambipom takes this to a higher level by having TWO prehensile tails, hence the name of the Pokémon being a play on the word "ambidextrous".
Deviluke's inhabitants of To LOVE-Ru, of course. Most of them, especially the females also can have Fantastic Arousal with their tails.
Kekkaishi has Princess, a Kitsune who has nine tails that she often uses to wrap an opponent to the point of nearly mummifying them.
In Bleach, Ulquiorra's second form has a tail which he uses for slamming people into the ground and holding people up by the throat, let alone the fact it looks like a whip.

The Moorwen from Outlander is a giant, lizardish thing, but its prehensile tail can be used to grasp, slice, or impale its victims.
Abu in Aladdin.
Maruti from The Return of Hanuman uses his tail once to grasp on a branch to hang on.
The cows from Home on the Range.
The vampire spawn from Van Helsing, which is weird because the parents are tailless.
Azazel in X Men First Class. It's strong enough to lift a person and sharp enough to stab them.
The aliens in Alien vs. Predator. Like Azazel, they can stab people with it.

Squirrels in the Redwall series hang by their tails a lot, which... no.
In Piers Anthony's Race Against Time, the protagonist first figures out he's not really living in a 20th-century small town when he discovers that his dog climbs trees and his kitten has a prehensile tail.
In Death Or Glory a young priestess of Adeptus Mechanicum has a mechadendrite attached to her lower spine. Useful to sit on (and freak people out, since it's hidden under her robes, and it looks like she's sitting on thin air) and steal snack bars.

The Fraggles have somewhat prehensile tails—they can be used as paintbrushes and can wrap around each other to play tug-o'-tails (like tug-o'-war, but with ... you know) According to the episode "Wembley's Wonderful Whoopee Water", they are also strong enough to support their owners' whole weight.
Power Rangers: More than a few Zords and monsters have prehensile tails. The Dragonzord of Mighty Morphin Power Rangers is one of the most famous.
Parodied in an episode of The Big Bang Theory. The foursome are playing a group roleplaying game as bad guys approach.

Leonard: They're on my tail! But it's prehensile so I can handle them.

There's a monkey in Dilbert who has an advantage over humans in the workplace because of his tail.

Tieflings in the 4th edition of Dungeons & Dragons can take a feat that gives them this. You can even pick locks or pockets with it.
- Multiple female Tieflings in Dungeons & Dragons works have made jokes about the myriad uses of their tails.
Star Munchkin has a Tailgun item only usable by Felines. What makes it notable for this trope is that the art depicts a normal-looking gun meant for hands curled up in a Prehensile Tail, not a gun specially designed to be tail-mounted.

As mentioned above, Aipom and its evolved form Ambipom are examples, both of which have hands on their tail(s). Their Pokédex entries specify some uses, such as shucking nuts, communicating (by connecting with the tails of other Aipom/Ambipom), balance (when leaping from tree branches), and attacking (specifically, with Double Hit, the move that enables Aipom to evolve into Ambipom). Many of Aipom's Pokédex entries also indicate that since it deftly uses its tail so much, its real hands have become rather clumsy.
Makoto Nanaya from BlazBlue: Continuum Shift slaps her opponent silly with her tail during her throw.
Two recruitable aliens in Albion use this as a separate equipment slot, capable of holding either a one-handed weapon or a shield (the former being the game's only instance of Dual-Wielding.)
Zidane of Final Fantasy IX has one, although he only used it once (to hang from the rafters of the pilot's cabin of an Airship).

Rhea from Slightly Damned, given the last name "Snaketail" because of this.
The superhero Katt O'Nine Tails from Spinnerette has nine of these due to a magical cat she once rescued. They double as Combat Tentacles as well.
In Goblins, Kin's tail is very agile and...sensitive. And strong enough to snap person's neck.

SCP Foundation: Dr. Bright considers this one of the reasons he likes simian bodies.
The Succubae from The Return.
Chakats have these.

Boots, from Dora the Explorer.
Xiaolin Showdown: The Monkey Staff gives this power.
Sometimes Scooby Doo's tail is.
Jake Spidermonkey in My Gym Partner's a Monkey naturally has one of these.
Gary The Rat's is used for Amusing Injuries because even though it is fully capable of moving around and grabbing things, he just drags it with reckless abandon.
Fifi LaFume in Tiny Toon Adventures can use her tail to grab "boyfriends", as a bat (As seen in Buster at the Bat), as a shield (As seen in the Defenders of the Universe licensed game), and to spray stink (Being a skunk and all).
In My Little Pony Friendship Is Magic, the ponies are occasionally shown to have prehensile tails, despite the tails apparently consisting only of hair. They are often useful for doing things which would normally be difficult due to lack of hands.
- Not that lacking hands seems to hinder them in any way. The non-mage ponies can make clothing, cook food, and do all sorts of other everyday tasks that would normally require manual dexterity, either with the aid of their teeth, or with just the plain hooves themselves (not sure if this is ever really explained). The unicorn-types just use telekinesis/magic.
- The Ahuizotl who appears as the villian of Daring-Do and the Sapphire Statue has a hand on the end of his tail, just as ahuizotls were said to have in Aztec Mythology.
Dino from The Flintstones, but it is shown less after the first season.