It is surely that Blip.fm is the NO.1 popular website for people to listen and share music to Twitter.
But not all the people like Blip, some people listen and share their love music to twitter from below 3 websites:
1. Last.fm
You have to pay for the music when the 30 free songs are used up, but it seems quite a few people would like to pay to listen what they love:

2. IMEEM
IMEEM is like Last.fm, you can search, listen and share the music or videos for free, that’s why I and (maybe) these guys like to use IMEEM instead of Last.fm:

3. TheSixtyOne
TheSixtyOne is quite like Blip.fm, it is also free for you to listen, to watch and to share the music, people like it for reasons:

So, from where do you share your favorite music to Twitter?
Related free web apps: