In the battle over the future of music between the likes of Rdio, Spotify, YouTube, et al., Last.fm has faded into the woodwork. It's still insanely popular, but hasn't kept up with the competition... at least, on the surface.
Dig into the backend, though, and Last.fm is a (if not the) powerhouse of music data. Its scrobbling service is baked into a huge number of music services, desktop and mobile players... almost anything that plays music nowadays can scrobble to Last.fm.
If you're not familiar, "scrobbling" is simply sending information about the songs you listen to to the service. I've been using it for years, and the major benefit is that, from the desktop music players that I used years ago to the web-based Rdio that's become my primary means of listening, all of the information on my music preferences resides on Last.fm. If, for some reason, I switched to a different player, chances are I'd still be able to send my data to Last.fm without missing a beat.
Many of those online services I mentioned earlier don't include a way to scrobble, though, which results in a skewed database.
This Chrome extension, simply called "Last.fm Scrobbler," can fix that. Install the extension, and when you visit a supported site (29, currently), give it the necessary permissions. Once you do, it'll do what it says on the tin: send your listening history to Last.fm. All the major services are here: Pandora, Deezer, Spotify, SoundCloud. Some obscure services make the cut, too: Bandcamp, Z-Music, TheSixtyOne.
When you're on a supported site, you'll see the extension's icon in the omnibox, displaying the status of its scrobbling prowess. Clicking on it enables or disables scrobbling temporarily.
Note that if you don't see one of your favorite sites supported, chances are the ability to scrobble is baked into that service, and therefore unnecessary (Grooveshark is a good example).
That's it. Now you can scrobble nearly anything you listen to on the web, ensuring an accurate music database. Now, if I could just figure out how to get Google Play Music on my phone to scrobble...