Maybe you don't know this, but on Pandora, you can choose more than 1 artist, and they'll play songs that fit in those genres, from all the artists you selected.
And, what I do, is "thumb up" all the songs I hear that I like, thumb down ones I don't, then that list becomes a new 'station' (It's called Thumbprint Radio) you can then choose, and it will still play other songs that are similar to the ones you've 'thumbed up.'
I have my playlist so curated by now, it's pretty much all I listen to at work.
And, if you can stand some short commercials, which don't bother me, since there's never more than 2 in a row, it's free.