GpDivx has had sound since Beta 0.3 - its just very very shite.
Or rather, it needs you to used uncompressed .wav audio at the lowest possible bitrate (1KB/s - 8kbs) mono.
But I don't think its still in development; if it is, then the next ver should be ludicrously feature packed since its been a year or so since its release.
GPMP might still be; don't know - *that* was a good player, but it may have just been written not as a free competitor to Moviepark, but as a demonstration as to how good the GP32 could get movie-wise. Unfortunately, the demo we've had released is limited to files of 6 and a half mins or smaller.
Moviepark is the best around for now - although unless another free player comes out, I doubt they'll bother to improve it hugely; when there's no alternative, and what's already there is good enough for people to buy, they won't continue development, as there's no need to. Or that's my take on things at least; could be wrong - perhaps a new ver is in the works...