Well of course if I was asking the question to others, would be pointless if I didn't :P
But it was The Beatles.
They also are the first and only band/act that has topped the top 5 spots at any time, i.e. all top 5 spots are their singles.
I was amazed I had no idea they managed that.
Overall they are the most successful band in the US to date.
Elvis and Mariah Carey comes a close 2nd.
And for even more amazements... Elton John beats Michael Jackson >.<