The story Mercury tells to lull Argus to sleep is the story of Pan and Syrinx. It is your basic "unwilling nymph transformed into vegetation" story, so there isn't a lot of variety in artistic portrayals. The main source of variety lies in how few garments the nymph is wearing and how much trouble she is having with them. Nymphs seem to have heard of clothes, but they haven't really grasped the idea and are very prone to what I believe is known as wardrobe malfunction.
The 1759 picture by Boucher (below left), now in London's National Gallery, shows the beginning of the story with Pan spying on Syrinx and another nymph. The painting by Jean François de Troy (1722-4) and now in Los Angeles's Getty Center (below right) is similar to the two paintings further below.
Below left is a painting by Jacob Jordaens (1625) now in Antwerp's Koninklijk Museum voor Schone Kunsten; and at right Nicolas Poussin (1637) now in Dresden's Staatliche Kunstsammlungen.
Arthur Hacker's 1892 painting now in the Manchester Art Gallery is different in that it only shows Syrinx in a reed bed as she starts to change. Pan is nowhere in sight.
The Louvre has a relief sculpture of Pan and Syrinx carved by Clodion (aka Claude Michel) in 1782.
Appropriately enough for a story of the origin of a musical instrument, musicians have also been attracted to this theme. This downloadable Word document (caution is advised) from the Amsterdamse Hogeschool voor de Kunsten gives the background to John Ernest Galliard's 1718 one-act opera called Pan and Syrinx.
The story has proved particularly attractive to 20th century composers. Debussy's Syrinx is very popular on YouTube. J. M. Ramos has put up his performance of Debussy's work on, appropriately enough, pan pipes, while Flutissima has put up her own performance on the flute, illustrated by works of art, not all of them actually featuring Pan and Syrinx. In either case, the 'related videos' panel will take you to many other performances of this work.
The Dane Carl Nielsen composed an orchestral work called Pan og Syrinx in 1918, which is downloadable from Amazon.
In 1951 Benjamin Britten composed a group of six oboe works based on Ovid's Metamorphoses for a fellow composer's daughter. The first in the piece comes from the story of Pan and Syrinx. The whole group of six works is available on a CD which includes performances of all six by the dedicatee, Joy Boughton, and a 2007 version by Nicholas Daniels, together with performances of Britten's earlier working versions by George Caird. Reviewed here. Britten's Pan can be enjoyed on YouTube (embedded below), again with illustrations, not all of which are strictly relevant.