the way my "collection" started, was by stripping old boards, looking up the parts, and saving what i understood, in the beginning it was mostly LED's and voltage regulators, but by now i have a small assortment, of shift regulators, opamps, 4000 series 74000 series, amplifiers and all sorts of stuff (little hint if you want cheap ass hitachi character displays, look for old fax machines, i think i got about 30 of those now, also handy with arduino).
i think about 80% of all the IC's i use, come from discarded electronics.
now i gotta say, i got a good job for that, as i work at a electriciens company, so i can get my hands on funky stuff like a digital phone routing cabinet from early 90's wich was stuffed with logic and dacs and stuff.