I bought an Iriver last week - the 40gb H340. I highly recommend it.
The sound quality is superb. I thought it sounded a bit flat at first, but that was before I fiddled with the equaliser settings in any detail. I'm not a huge audiophile, but I have decent standards, and I was blown away. So much so my girlfriend - a real tight-ass who hates my "gadget-buying" habits - went out and got one too (20gb version). I think that's a real sign that it can wow the average user with the quality difference in sound. The pack in headphones are small Sennheiser buds, which I've never used but Megan actually commented that she can't go back to her old Sony 'buds. (I have Sennheiser HD280 pros, external noise dampeners).
To top it off, it has a colour screen which can show images and play movies! Movies have to be encoded specifically, but there's heaps of free software on the net to do the job. Movies on the go might not be something you'll use a lot, but when the similar-priced Ipod doesn't do it, it's a no-brainer to me.
It's plug+play with Windows 2000 and XP. Your device comes up as a hard drive. It can store files for transfer on any WinXP/2k pc without drivers.
It supports "USB on the go" which means I can plug my camera into it and transfer files off of it. I'm going to Japan next month, and I'll easily fill my 1gb SD card. Now I can transfer them all to my Iriver on the go as it fills!
Inbuilt voice recorder in either MP3 or WAV. It also has microphone support (comes with a small mic). I bootleged a concert last night with it, and while I wouldn't say it was great, it was easily on par with other bootlegs you find on the net.
Finally, there's a decent-sized community developing for it. A Rockbox project is in the works, which actually looks like it will support GNUboy! That's also going to mean it's a Gameboy. Try
www.misticriver.net for more user-information.
To the fellow complaining about Iriver's volume levels, make sure you have updated firmware. Like a number of other players on the market, it's a "safety" feature. Safety can sod-off, thank you, I like my music LOUD. With my headphones flipped out, I use my iriver for external music at work.
If you've got any questions, I'll be happy to help answer them. But keep them in mind - you don't seem to be considering it as a serious option, which I think is a big mistake.
Cheers