all of these are great entries - it's interesting (to me) that the modern day "transistor radio" is the mp3 format itself, or at least projects that are inspired by playing mp3s, lots of those.
overall, here are my picks.
cvs_camcorder_hack
http://tcashcontest.pbwiki.com/index.php?wiki=cvs_camcorder_hack
it's the most documented out of the bunch, you can not only go do this now, but you could use this article to get going from start to finish. it's not "new" but all great things are built on other things, this rolls up all the good work out there.
the compression chuck hack
http://mtnmck.pbwiki.com/index.php?wiki=CompressionChuck
this hack is a homemade tool to make other things and that's always a plus.
nick k guitar hack
a great hack, because it's modding something to work better or different.
of course, i should say, they're all great - excellent work.
cheers,
pt
www.makezine.com