what everyone said, but specially Tetsuox - I'm crazy mad at bugging people for the names of songs - in shops, at peoples homes, on the bus. and I used to shazam everything back when it was text 2580 hehe... and then hearing stuff on tv and finding out what it was. and then I sample off old cds and any mp3s i can find. youtubes okay, but the sound quality used sound youtubey - its got much better now, but theres nothing better than finding an old record or even dusty cd and knowing its not on youtube.
this track i made uses 9 samples from way different places - film sound tracks, old records, some snippets from old tv theme tunes, random mp3s and some old cds... any sound you have electronically can be sampled... you just gotta cut filter, speed up slowdown to fit. and for most tracks that I build with many many samples, I try maybe 20 potential samples before I find one that goes. and even that might not cut it when I sequence. the track I just posted, I tried maybe 100 samples for different bits (diff drums, bass, differnt everything) and all of them had to be played around with and manipulated just to find out they don't "work"... it takes hella loada time, but its so fun...