Well, the name who jumps up first above all others is Stanley Weinbaum....
Weinabum died in '36, and was for the year before his death the biggest name in short SF... Asimov famously said something like "If Weinbaum hadn't died, John Campbell wouldn't have mattered"...
There's some absolutely fantastic stories in his archive, particularly A Martian Odyssey which is regularly listed along with Nightfall as the greatest short SF story ever (bit long for audio tho).
The problem with Weinbaum is his PD status is a little ambiguous... US law puts all American IP from before 1924 as still reserved to the holders, which is why people like Lovecraft (70 years dead) haven't crossed over into the public domain yet. His archive has been given to the libarary of Congress, and his collected works can be found on the Australian Project Gutenberg site, but unless you can find an unambiguous handover of his IP by his family then it's probably still reserved (although not enforced, whereas Lovecrafts IP is rigorously enforced by "Arkham House", bunch of bastards).
The problem you'll find is that, before Weinbaum, SF was pretty unsophisticated. Unless you want to read out Frankenstein twenty times, you wont find anything worth using...
Weinbaum is unusual in that he wrote a LOT, in a very, very short time, then died almost immediately... That would be perfect, and no one else is close, but personally I wouldn't risk it.