Soundclick is the **** if it's sheer volumes of music you want to upload. I think you can post unlimited songs on there. I've certainly seen bands up in the hundreds.
HOWEVER, it is a bit of a **** to use if your target audience are not soundclick users, as non users can only receive low-bitrate ( < 96kb/s i think) streams, and can only download, or hear in full quality if they sign up. It's free and ****, but it's usually more hassle than most people are willing to go to.
As a guideline for what many people do, you put your best 4 on myspace, and promote it most, but use soundclick as well in order to have a more extensive back catalogue that you can direct your more "dedicated" listeners to.