The new Rio Riot (20GB and FM tuner for $400) and Nomad Jukebox 3 (20GB, firewire for $350) can be serious competitors in the hard drive mp3 player market (especially since those two have PC compatibility). I'm not saying they're better than the iPod, but they could take a serious chunk of potential iPod buyers.
As a matter of fact, price is the only reason why I don't have an iPod in my hand right now. If it went down to the $250 range (around where many of the 6 and 10GB players on the market are), I'd buy one in a second.