Good Lips, Evil Jaws

In a work of fiction with many kinds of fantastic talking critters, how can you tell are on the side of good and which aren't?

Simple, the good guys have expressive lips and the bad guys have scary, protruding, teeth. Commonly found in reptiles and the undead.

Examples of Good Lips, Evil Jaws include:

Film

Ice Age 3: The good Mommy dinosaur vrs the Albino DinoMonster.
The Lord of the Rings has a lot of Orcs with no lips at all. They're humanoid, and besides just being ugly look fairly normal..they have rather human mouths, if unusually sharp teeth, but these mouths are not covered by lips.
Antz does this with the Termites.
Dinosaur and the... well, ALL the non-friendly dinosaurs. Conversely, the iguanodon protagonists were originally designed with rigid beaks, which would have been accurate, but they were later given lips in order to make them more expressive.
Alien of course made sure everybody knew their monster meant business and gave it two sets of mouths each with razor sharp teeth. It does have lips, but they're usually peeled back in a snarl or hiss.
The Transformers Film Series plays with this, with the Autobots having humanoid looking faces and mouths, while the Decepticons have more beast/insect-like heads with fangs. A good comparison would be Optimus Prime and Megatron.
In Resident Evil Apocalypse Nemesis (who has humanoid, yet huge, teeth but no lips) subverts it by being a remote-controlled Tragic Monster and eventually turning to the good side.

Dracula in the book had two front teeth stick out on rest on the lips. Characters after been bitten will slowly end up showing more teeth protruding from their mouth until they turn.
- Naturally Nosferatu follows in the same vein as Dracula.

Averted with Farscape. The creature designs are highly varied, and there are plenty of individuals on both sides of the good/bad divide with lips and fangs all over the place.

Dungeons and Dragons 3.5: The dragons are represented this way. Evil, chromatic dragons have long fangs and sharp teeth that show even with their mouth closed. Good, metallic dragons have closed lips and none of their teeth show.
Hordes features the Legion of Everblight. Its dragonspawn warbeasts are best described as unholy offsprings of Xenomorphs and dinosaurs or winged snakes, and they all share the same nasty, nasty lipless maws. Then there's Typhon, basically the setting's Hydra.

The Super Mutants in Fallout 3 don't have any lips and only have their teeth showing.
Subverted with the Orcs and Trolls of the Horde in World of Warcraft, who have prominent tusks (the males do, at least) but are just as likely to be good or evil as the rest of the races portrayed in the game.
- This also applies to the Alliance's worgen, whose sharp teeth are always on display.
In Dissidia Final Fantasy, every character has lips...except. Chaos has only very sharp teeth showing, and then in Duodecim Feral Chaos takes this Up to Eleven. Speaking of Duodecim, the villains Garland and Exdeath have reskins that invoke this. It's hard to tell whether they are in fact lipless or if they have lips but are just constantly baring their teeth, but the net effect is the same.

Inverted in Myth Adventures the Comic, Phil Foglio's illustrated version of Robert Asprin's books. One of the two main protagonists, Aahz, has a huge mouth full of razor sharp teeth - and he's the good guy. (Well, sorta...)
- He's also described like this in the books - the main factor about Phil's illustrations is that it actually captures this, while most of the covers opt to go for a more conventional fantasy-genre cover which depicts the characters in a "realistic" (read: boring and with all the vitality of a store mannequin) style, where Aahz is depicted as a bald human covered in green scales, and even when his mouth's open his sheer toothiness fails to come across.
- Phil Foglio actually does this a lot. Multiple heroic characters in such diverse works such as What's New with Phil and Dixie and Girl Genius have More Teeth Than the Osmond Family, occasionally with no explanation whatsoever.