Does anyone know of anything similar to Pandora, in that you can put together your own station?

I really like the idea of Pandora, that it can take your variety, put it into one station, and then throw in their own additions that are similar to your own picks. However, their library is dwarfed by several other sites, and I would like to take advantage of a larger library if possible.

I use Spotify and Google Music, but they only have the pre-programmed stations, as far as I have found. I am hoping I am wrong and one or both of these have a way to make my own mixed station. If they do, please let me know how!

Anyway, has anyone heard of anywhere that tries to provide suggestions or similar songs? I like a wide selection of music, and Spotify and GMusic both seem to have overly specific playlists/stations for my liking.

Thanks all for any help!