From podiobooks.com I really enjoyed
Singularity, by Bill DeSmedt.
Also the "Golden Age of the Solar Clipper" trilogy -
Quarter Share,
Half Share, and
Full Share, by Nathan Lowell. The POV character might be a bit too much of a Wesley Crusher, but it kept me engaged.
Brave Men Run by Matthew Wayne Selznick. Sort of a "Breakfast Club" meets young X-Men
The Plitone Revisionist was an entertaining sort of space opera.
People go on about
Earthcore, but I couldn't make it past episode three. Just didn't do it for me, but I might go back to it a couple of months from now.
If you like the classics, there's always
Librivox, if you don't mind that some of them have uneven recording and reading quality. All from public domain texts, usually pre-dating 1923, but there are a few PD SF works that were originally published in pulps.