I've been moderately obsessed with this for a couple weeks now. Billboard just hit 1,000 number one songs (Lady Gaga's "Born this Way"), and I think I could teach this list as an American history class.
Stream all 1,000 songs over at Billboard's website.
Or, if you don't have that much time, here is an incredibly addicting proposition: five seconds of every Billboard #1 ever, in order:
Five Seconds Of Every #1 Pop Single Part 1 by mjs538
Five Seconds Of Every #1 Pop Single Part 2 by mjs538
5 Seconds of Every #1 Billboard Hot 100 Hit From 1993-2011 by AnthonyDC