I've got one of those new iRiver H10s with the 5 Gb microdrive, and I like it so far. It's got a pretty simple UI, quasi-USB Mass Storage capability, and super good language support, and looks/sounds pretty cool too, and also has a touch sensitive scroll bar thing (opposed to the ipod mini's touch senstive scroll wheel), plus the FM and recording, and photo viewing and all the other crap iRiver adds to their players.
Only disadvantage to iRivers are that it must be the only company (other than maybe Sony) to consistently retail their products with HIGHER prices than Apple. I was lucky enough to score the H10 for like $180 via the Napster promotion, but as long as iRivers are so expensive, I don't see them as a major player in this segment (unlike Creative, whose players are cheap(er) and also decent).
In the end, it will come down to the cost and personal preference. I hate to admit it, but the ipods are a decent deal, considering it's apple. Probably the least price inflated thing apple makes (unlike their computers/laptops/lcds), but I just dislike apple for some reason, and got the iriver instead.
As for napster, it's not too bad. Although I liked it better when I, er I mean other people, could easily circumvent their DRM 🙂. Too bad napster is pretty agressive in maintaining the security of their rental music.