ok im back from maker faire and PCBs arrived so ive released my wave shield for playing audio. it reads wave files (uncompressed audio) from a formatted SD card
there's schematics, documentation (which is almost done 
) , libraries & example code!
i also made a kinda sucky video. woooo!
www.ladyada.net/make/waveshield
That's neat. I calculate about 30 minutes of good-quality audio on a dirt-cheap 64MB flash card. It's a bit of a shame that the SD socket takes up so much of the physical space, and the FAT32 code takes up so much of the code space, but's it's not awful...
I've often gone to zoos and similar and been depressed at the often-broken state of the audio-playback boxes they sometime have to provide explanations. And then I get depressed about how much abuse such a box has to actually put up with without breaking, if it's going to be better. Something like an Arduino with this playback board, and some sort of non-mechanical sensor (capsense, optical, etc) might go a long ways toward making such things really reliable. And with an Arduino in there, there would be the flexibility of interacting with other sensors and actuators as well. In a relatively standard way.
I wonder how insular and defensive the "exhibit electronics" business is?
well, sd cards are very small compared to -compact flash- cards, which is what ive worked with before. there are mini-sd and micro-sd cards but man, those are small, harder to solder/work-with/not-swallow.
i didnt need more room so thats ok by me!
That is impressively simple! Ill have to spend more time looking at your design but I already want to make a standalone board. What is that something like 9 io pins? Combine this with a t class chip amp and then you could rattle walls! ;D
Cheers,
B
I was thinking the audio card could have its own ATmega chip, and you'd send it "play foo.wav\n" style commands, but I didn't see room for another chip. 
A device with SD socket can use miniSD and microSD cards as well, via the ubiquitous adapters, so that's cool too...
if you want to do that, you can use a vmusic2 module.