(This is my first post, but I've been lurking for a while)
The first thing you should keep in mind is that there is no "best" mp3 player. I personally own an ihp-120, and I feel it's the best for my needs, but it could still use a lot of improvement.
Creative makes two portable mp3 players which are worth considering. If you don't mind lugging around an mp3 player the size and shape of a large PDCP then the Creative NJB3 is a good choice. It (apparently, haven't heard it) has the best sound and has over 20 hours of battery life. Creative also makes the nomad zen players, which have good audio and battery life(15 hours), but are bulkier than the ipod, ihp, etc.
Two other players worth considering are the iPod and Rio Karma, both of which sound good. However, the ipod only has around 8 hours of battery life, compared to around 15 for most other players and the Karma seems to be more prone to failure than other players. Both of these players have a line out on the dock, but not on the player itself.
DAPReview has a lot of information on mp3 players.
BTW, I think bangraman's digital upsampling headphones need a toslink connector, which isn't present on the echo indigo or on most mp3 players. The ihp has optical line in/out, but bangraman disliked the sound quality enough to return his ihp.