The simplest thing, IMO, is just to buy your music on CD and rip it to a free format yourself. Some indie artists release their work online in free formats, but for mainstream artists a physical copy is often the only way.
In the UK format shifting was briefly allowed but media corps objected and the Tories decided it was better for society not to be able to rip CDs you own. iTunes, f.e., is a tool for contributory infringement in the UK.
I'm not saying it is ideal, but the used CD market is hugely depressed right now. I buy a ton of used CDs at various downscale businesses and rip them into iTunes with Apple Lossless. Some of the stores will run them through the disc cleaner/polisher as a matter of course and they rip fine.
I'd love to be able to buy DRM-free 24/96 lossless versions of all the music I actually want but buying used CDs for under $2 apiece seems like a reasonable compromise to me. For the moment if I can't find particular albums on CD in the used market I either buy them from eBay sellers or do without. The remaining chain retail vendors for CDs such as Best Buy have a pretty hopelessly bad selection these days.
The question was specifically "Where can I find Rihanna in Ogg/Vorbis?" Rihanna is not on Bandcamp, so this is a pretty poor answer. You're essentially telling people to like different music than they do.
