Scylla

In Eclogue 6, we have (74-7):
quid loquar aut Scyllam Nisi quam fama secuta est
candida succinctam latrantibus inguina monstris
Dulichias vexasse rates et gurgite in alto,
a, timidos nautas canibus lacerasse marinis

As Williams notes, Virgil seems to be conflating the two Scyllas, which happens in several other authors (1996: 118, n 75f).
Lucretius says (5.892-3): aut rapidis canibus succintas semimarinis/ corporibus Scyllas et cetera de genere horum, "or Scyllas girded with fierce dogs on semimarine/ bodies and others from the type of these."

Propertius says the following (4.4.39-40): quid mirum in patrios Scyllam saevisse capillos,/ candidaque in saevos inguina versa canis, "What marvel (is it) for Scylla to have raved over her father's hair,/ her dazzling groin turned into savage dogs?"

Ovid in his Fasti writes (4.500):  et vos, Nisaei, naufraga monstra, canes, "and [she fled] you, Nisaean dogs, shipwrecking monsters."

In Ovid's Metamorphoses, we see a similar description of Scylla, neatly wrapped up in the story of Galatea and Polyphemus.  You will recall that this story was in Theocritus and alluded to in previous Eclogues.  Ovid's initially says Scylla latus dextrum [infestat], "Scylla injures the coast on the right" (13.730), setting up a parallel with Charybdid laevum.  He then describes Scylla:
illa feris atram canibus succingitur alvum,
virginis ora gerens, et, si non omnia vates
ficta reliquerunt aliquo quoque tempore virgo.
Hanc multi petiere proci

That one is girded with wild dogs as to her dark paunch,
bearing the face of a maiden, and, if the poets have not left
all fictions, also, at some time, was a maiden
Many suitors sought her

Ovid goes on to say that Scylla rejected the suitors, and bragged to her nymph friends about her elusiveness.  Hence, Galatea shares her story.

After this, Glaucus's metamorphosis is woven into Scylla's story.  He, a once mortal recently turned sea god, chases Scylla.  When she pauses, he tells her his lengthy story, and in the middle of it, she gets up and leaves.  Angered and annoyed, he goes to Circe for seemingly a love potion (if I read that correctly).  She, however, expresses her desire for him.  Glaucus, unfortunately, maintains his love for Scylla, and Circe, since she still loved Glaucus, decided to harm Scylla instead.  Circe uses her potion/drug/magic juices to pollute the area where Scylla is, and the following transformation occurs (14.59-67):
Scylla venit mediaque tenus descenderat alvo,
cum sua foedari latrantibus inguina monstris
adspicit ac primo credens non corporis illas
esse sui partes refugitque abigitque timetque
ora proterva canum, sed quos fugit, attrahit una
et corpus quarens femorum crurumque pedumque
Cerbereos rictus pro partibus invenit illis:
statque canum rabie subiectaque terga ferarum
inguinibus truncis utero exstante coercet.

(I'm just going to give you the Persus translation of this one, rather than translate it myself)
Scylla came there and waded in waist deep,
then saw her loins defiled with barking shapes.
Believing they could be no part of her,
she ran and tried to drive them back and feared
the boisterous canine jaws. But what she fled
she carried with her. And, feeling for her thighs,
her legs, and feet, she found Cerberian jaws
instead. She rises from a rage of dogs,
and shaggy backs encircle her shortened loins.

Book 8 of the Metamorphoses tells the story of Nisus and Scylla, as does the story, Ciris, which I couldn't find.