RhythmArty is a Rhythmbox plugin that allows you to browse your music collection via album art. I didn't post about it until now because it initially (versions 0.1 and 0.2) crashed my Rhythmbox (you can see comments related to this here) and then when version 0.3 was released it did work but it was very slow with my ~30.000 files music collection.
But today, RhythmArty 0.4 was released which not only fixes the crashes but is also very fast and works great with large music collections. Besides the performance improvements, the new RhythmArty also got a new option to fetch the missing cover art (Tools > Get Covers).
The current RhythmArty features include option to customize the colors, set the cover art size and easily toggle it on/off via a button on the Rhythmbox toolbar.
One annoyance in RhythmArty, at least for me is that a lot of albums don't have cover art so the standard RhythmArty cover is used. One way this could be improved would be to use some artist picture instead of the album covers in such cases.
Download RhythmArty (includes .deb and source files)