Hello killinsound, the Yamaha P120 ia a really good digital piano, it has a great sound, but if you are in a tight budget, it's smaller brother, the P60 has graded action, selfcontain speakers, headphone output, midi I/O, and only a handfull of sounds...for under $700.00.....Casio has 2 models, one with no arranger functions, and the other has, one is under $500.00 and the other under $800.00...
I also recomend you to check for descontinued models that a music store may have, like the P80....perhaps a Roland series F ( portable and with beautifull sounds/action),series HP....(the HP is not portable), and probably with an atractive price too. Good luck.