I have ditched Google Music's Web player for Radiant Player, a standalone Mac app that lets me access and control Google Music via my Mac's menu bar and media control keys. If you use Google Music via a browser, however, and dislike having to return to the Google Music tab to control your musical proceedings, then you should know there is a Chrome extension that lets you control the action without leaving your current tab.
The awkwardly named but subtly useful Music Bubbles extension for Chrome places a small, floating control on your current page. And when you reload your current tabs or open new pages, you'll find the Music Bubbles control floating on them, too.
The Music Bubbles control is a transparent circle, which allows it to remain omnipresent without being overbearing. It's gray in color when you do not have Google Music opened and turns orange when you do have it going.
Mouse over it and play, skip back, and skip forward buttons spring forth, along with thumbs-up and thumbs-down buttons. And if a song is playing, you'll see the song name and artist below the Music Bubbles control.
Perform a long click on the Music Bubbles control and the thumbs-up and -down buttons retreat and two black buttons appear in their place. The one on the left lets you drag the Music Bubbles control to reposition it, and the one on the right lets you blacklist the current site so that the control does not show up when you visit the site. You can then edit your blacklist in the extension's options.