I do a lot of scrounging.
Admittedly I just like taking things apart, so the motivation is not always to get useful parts.
But once you have a large junk box full of old circuit boards you just know that one of them is carrying the part you need.
Conversely, I often find myself staring at a board and wondering "what the hell is that thing?"
I have a pretty good basic knowledge of electronics, and I think I can identify the general class of a part without much help, but there are always mystery items which need some research.
I like research.
What better way to waste time then by learning something?
Along the way I have collected a few links which I use to try and figure these little mysteries out.
Here are a few:
The impressive sounding FCIM Component Identification Tool it is at least 12 years out of date, but then a lot of the things I am scrounging from are old too. The site is hard core Web 1.0, and a little hard to navigate, but they show LOTS of useful info on package types, general usage guidelines, and part numbers.
For a newer resource that includes lots of surface mount (SMD) codes try TKB-4u (The Technical Knowledge Base for You!) which lists lots of codes, and some basic info on identifying those tiny parts.
There are more lists of SMD parts at TALKING ELECTRONICS as well as useful information on op-amps, voltage regulators, opto couplers, and some basic older ICs.
For semiconductors, once you have found the part number you will also need to know how to use it, and for that you need a data sheet. Data sheets are like gold. They have the pin out, all the power specs, timing data, and often a reference circuit you can use as a starting point for your own designs. Finding a data sheet for an older part can be difficult, and many of the site which claim to have them want to charge you for them. Some time ago I discovered All Data sheets and have rarely had to look anywhere else.