Generally speaking, I just wing it, but how much effort I put in depends on where and when the loot was found.
If the loot was found in a random encounter and the whole purpose of it all is to be sold at the first chance, I'll make that clear: "You find a small hoard of gathered trinkets. A lot of it is junk that the monsters accumulated, but some of it might have resale value once its been cleaned up and repaired. You're fairly sure you can find someone willing to give you about X for the lot." Where X is an appropriate number based on their appraise rolls and the random monster they faced.
For monsters that it doesn't usually make sense to have treasure, I try to cut the PCs some slack and usually tell them "Well, you know that there are all sorts of people who would pay you for parts of this thing." Alchemists used to be a personal favorite for the "types of people" but then the alchemist class came along and a Player started running them, and next thing you know he's asking "well, what do the other alchemists want them for? maybe we shouldn't sell them and I can use them..." Which isn't actually a bad thing, but did lead to me accidentally upsetting the game balance once or twice, and having to remove certain monsters from the random encounter lists.
If the loot belongs to someone important (as in, a Named NPC), then I'll try to come up with what sorts of things he collected, and describe a few specimens of the horde. Because I know my group well enough to know that they like to take trophies, I'll always try to come up with some little curio they can find and keep which will usually end up being prominently displayed and talked about by them in the future. I've found this also helps to cut down on the walking gore-fest factor: Given the choice between a stone tile that always floats just within arms reach to their left, but can only support a full goblet of wine before it stops functioning and falls, or the ears of its previous owner, I can usually count on most of my PCs to go with the magic coaster.
The other thing I do, when I'm looking for random specific things, is I look at the focus and expensive material components for various spells, and then toss those into the loot, deducting their GP value (which is often helpfully provided in the description). Even for spell-less baddies, this doesn't really need much work to justify: They took it from a spell caster, or maybe it was an heirloom and they didn't know what it was for. And I've yet to have the party who failed to feel it was worth it to keep that small handful of diamonds, rather than sell them and buy some more magic gear. Sure, it might have only been part of a Resurrection spell, but it was part of the resurrection spell.
