Here's a great resource:
http://donjon.bin.sh/5e/magic/shop.html
Let's take a snapshot of an example Shoppe (Large City):
Location: On West Court Road, in an adventurers quarter of comfortable inns and bold explorers. The street outside is filled with the scent of burning wood.
Description: The shop is a single storey stone-walled building, with a slate roof and a tiled mosaic floor. It is dimly lit by a few candles and fairly shabby.
Shopkeeper: The shopkeeper is an overweight male half-elf named Rarder Wesell. He holds a grudge against humans.
To this I'd add a
Guardian: entry, knowing how players are...

But I digress. Wesell's inventory, sorted on asking price:
+1 Weapon (quarterstaff, rating 3) (dmg 213)
Asking Price: 500 gp
This finely crafted weapon is said to lead the one who wields it to wealth and glory.
Potion of Heroism (dmg 188, rating 16)
Asking Price: 1,150 gp
This clear liquid smells like cedar.
Necklace of Fireballs, 3 beads (dmg 182, rating 8)
Asking Price: 1,550 gp
This finely crafted item was taken from the hoard of the dragon Milki.
Oil of Slipperiness (dmg 184, rating 12)
Asking Price: 1,750 gp
A ruby liquid, contained in a steel phial sealed with wax.
+1 Ammunition (20 sling bullets, rating 9) (dmg 150)
Asking Price: 1,800 gp
Foes slain by this weapon are consumed by flames.
+2 Weapon (maul) (dmg 213, rating 5)
Asking Price: 2,400 gp
Every strike by this weapon is accompanied by a monstrous snarl.
Cap of Water Breathing (dmg 157, rating 11)
Asking Price: 3,000 gp
This battered item was created by a goddess of magic for her most loyal champion.
Iron Bands of Bilarro (dmg 177, rating 7)
Asking Price: 4,800 gp
This distinctive item once belonged to the great hero Eron, who perished in the Northcrown Mountains.
Stone of Controlling Earth Elementals (dmg 205, rating 10)
Asking Price: 20,000 gp
This finely crafted item once belonged to the illustrious hero Fertio, who defeated Lord Greywulf.
+2 Armor (breastplate) (dmg 152, rating 14)
Asking Price: 29,400 gp
This distinctive armor is said to have been blessed by the Goddess of Luck herself.
Wand of Paralysis (dmg 211, rating 18)
Asking Price: 129,600 gp
This thin wand also grants the magical ability to feign disease or illness for one hour per day.
That didn't take long, maybe half an hour.
All prices rounded to nearest 50 gp. Obviously, the ratings would not be given to the players or their heroes - I've included them for your benefit. What would
you buy, given a good-sized bag of gold...?
