Sony's new MDR-XB50BS Extra Bass Sports Wireless in-ear headphone is worth considering for a few reasons: Not only is it relatively inexpensive at around $60 online (£60 or AU$130), but just as importantly it fits well and sounds good, particularly if you listen to bass-heavy music.
A bit clunky-looking, it isn't the smallest in-ear wireless headphone, with a footprint around the size of the(which is, in turn, three times more expensive). However, it's fairly lightweight, and fit me better than the Powerbeats3, though the Powerbeats3' ear hooks are beneficial in keeping the earphones on your ears.
The MDR-XB50BS comes with a few different size fins and eartips, and I was able to get a nice tight seal with the large size of both, and that seal was crucial for maximizing bass performance. This is a noise-isolating headphone and it does passively muffle ambient noise pretty well, so you won't be able to hear traffic while you're running if you're playing your music even at moderate volume levels.
Speaking of running with these earphones: While I got a snug fit and the headphones stayed in my ears just fine walking around New York City and while lifting weights at the gym, I did notice a little bit of slippage when I ran with them. For me anyway, the fin wasn't locked in my ear quite as well as I thought it was. To be clear, everybody's ears are shaped differently, and these may lock very well in your ears. But I'm just passing along my experience, which left me with some doubts about whether they'd be the perfect fit for runners.