Having just gone through the debate myself of whether to buy an iPod or a Zen, I'm going to throw in my 2c and say that the Zen came out looking far better than the iPod. Agreed, the Zen's interface isn't as 'sexy' as the iPod's, but I found the side jog-dial much easier to use than iPod's front wheel (easily navigable with one hand). Also, I found the iPod to have an over-sensitive touch...the Zen feels more reassuring.
All the above is my opinion, but noone can argue that the Zen has about 4 hours' more battery life than the iPod. Furthermore, the Zen has a more powerful on-board amplifier (100mW vs. 60 mW max output), which was better able to drive my Grado 60s. (Granted, both sounded far better with an Airhead, even though the Zen doesn't have a line-out).
Finally, should 20gb end up being insufficient space for your mp3s, the Zen is fairly easily upgraded (merely swap out the native drive and replace it with a 9mm laptop harddrive of larger capacity).
Yes, the native software of the Zen is crappy. But for $25 you can get Red Chair Software's Notmad which is every bit as good (if not better than) the iPod interface. Given the amount you'll save on the Zen, the extra 25 is more than worth it.
The iPod is certainly the cooler looking device...but that's where its advantage ends. Not only is the Zen a better value, it is an all-round better device (IMHO
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Peace to you and yours.
-88keys