You know, with a laptop, you could easily be talking about the GW-8...
Cheap, light, no speakers, good sounds, live style mode, mp3 playback, SMF playback.
Only disadvantage is that the Playlist editor, to put together different chains of songs, is a software thing, so to change it on the fly might be difficult...
A was VERY impressed with it, at the price point it was... I already have a G70, so it's not anything I need in particular (unless I was hiking with it!

), but if I didn't have anything Roland, I think this is what I would get to get the best bang for the buck right now.
It truly is an impressive sound set at that price, forget all the arranger and MP3/Wav/Aiff stuff it can do too... All that Latin stuff is just the icing on the cake...