I recently purchased the 6GB Sansa e270R and highly recommend it. This model is also know as the Rhapsody MP3 Player.
The Sansa is a flash-based player with roughly the same form factor as an iPod Nano and, like the Nano, has a color screen and can display photos so it competes for a similar audience from those perspectives, but the two devices go in very different directions from there. Although the Sansa is capable of storing and playing owned content just like the Nano, it is also capable of playing subscription content. It also has an FM tuner and integrated voice recording capability (good luck finding a use for this in it's current state - i.e. you need to talk very loudly directly into the player to get a usable recording).
As you may know, Rhapsody is a subscription music service and application from Real. Yes, I know RealPlayer (another Real application) is less than popular with many people, but Rhapsody is generally rated very highly. Although Rhapsody is both a service and a standalone application, there is also a web based front end available (it doesn't have all the same functionality as the standalone app).
The recent 4.0 release of Rhapsody coincided with the release of the new Sansa and Sonos Music System 2.0 (more on that in another post, perhaps). As can be seen on the support forums, 4.0 has knotted the undies of some existing users, but I suspect it is more approachable to new users.
The main theme of 4.0 is music discovery. Music discovery is the main reason I like a subscription-based service over an ownership-based system like iTunes so I think 4.0 is great. I like to listen to a wider variety of music than I can afford. I also like to listen to specific music for a relatively short period of time and then perhaps only occasionally (I've got a 200-CD jukebox full of music at home, but I rarely listen to any of the 200+ CDs I own). For these reasons, I don't mind paying a monthly fee for music I will never own.
Rhapdosy has had a feature called "Channels" since I started using it. A pre-defined (by Rhapsody staff) channel covers music specific to a genre. A user-defined channel can be created by specifying artists whose music, and similar music, you want to hear. For example, I like Miles Davis so I created a Miles Davis channel. On that channel, I hear music from Miles Davis, Charlie Parker, Dmitri Matheny, etc. One of the new channels available with 4.0 is "My Rhapsody Channel". This is an auto-generated channel based on recent listening history and the ratings you've given music.
With 4.0 these channels can now be transferred to the new Sansa. With this feature, roughly five hours of music per channel is available on the go! And the content of a channel can easily be updated when the player is plugged into the computer.
Dynamic Playlists are another new 4.0 feature. These playlists are editorial-generated (i.e. Rhapsody staff generates them) and updated on a regular (I don't know what "regular" means in this case) basis. Some of the playlists feature the top 25 tracks (based on the listening of all Rhapsody subscribers) in specific genres (e.g. Alternative Hits). Others are Rhapsody recommendations or some other theme.
Like other playlists, Dynamic Playlists can transferred to the Sansa. Unlike other playlists, Dynamic Playlists on the player will update automatically whenever the player is plugged into the computer - pretty cool. (Dynamic Playlists are a feature I craved after noticing it in Microsoft's new Urge service when I briefly looked at a beta of it a few months ago.)
I used to listen to Rhapsody channels while working in my office, but recent network changes have included blocking of all streaming audio. Now, I just load my Sansa up at home, bring it to the office with me, plug it into my speakers and I'm set. Even though I'm only using half of the 6GB capacity, I can listen for days without needing to worry about synching the player to reload it with content.