The Cowon S9 doesn't have expandable memory, but the J3 does. They're basically the same thing other than that. You can also look into the nationite s.flo
In my personal opinion, the nationite S.flo is very close to the J3/iaudio 9 in sound quality, although the s.flo probably has a slight edge over Cowon. Some things to consider are that the S.flo has a dedicated line out, which the J3 and S9 don't, but Cowon does have bbe sound enhancements which are very nice. The user interface on the J3 is much better than the S.flo, and the touch screen is faster to navigate on as well. The cowon players are overall more modern, the S.flo is sort of a hardcore audiophile player.
The sansa fuze/clip are good choices as well, but aren't quite as nice as the Cowon or nationite players in terms of SQ although that's to be expected as they're only about half the price. Once you get rockbox on the Clip it's very nice though.