Here's a method I just came up with that's going to speed my mapping up a lot,
you'll know if it's the one for you or not. The earlier you start using it, the more time you'll safe.

The only current way to place a model in a map is to use entity + prop_whatever. My problem is the waiting. The prop previewer starts automatically loading/scanning all props, alphabetically arranged, you never get what you want fast enough. The premade folders aren't perfect, and most of the time I find myself browsing through all folders and googling for item pictures and trying to come up with a corresponding name that fits what I'm looking for.
Good example:
I couldn't find the oildrum for untill foyleman told me it was NOT to be found with what I was searching it: keywords barrel and gas...

So... what I have in mind is simple.
Props that you think you use a lot, like oildrums, crates, fences, lamps, lights, trees, stuff you know you will use in most maps:

SAVE THEM AS PREFAB !

This is awesome, you can name/arrange them a order and way that makes sense TO YOU ! You can even create your own subfolders in the prefab folder.
You remember best what stuff you prefer to with what name,
and what category it should be in.
The benefit is no more loading time ! Just shift + e, select the category you saved the prop in
(default are "entities", "prefabs", "prefabs HL2"), pick the item name from the list.

I'm sure you'll find it faster than browsing around in the prop-previewer. This of course works only best when you know what you want to use.
A bonus is that you can add lights/env_glows/spotlights/sound
and much more effects to them, so you don't have to worry placing them all over again either!
Very handy for lamps and light props !

So, where's my Nobel prize...prise...price.... how do you spell that one again ?

WARNING: 99% chance of hammer crashing when you first time save a custom prefab in a new subfolder, other than the default prefab folders !

a great idea.

except that you will have to include a resource that already exists in the game when you release your map to the wild, as the directory structure (path)will be different than where it exists naturally

this will needlessly increase your distributable data size