As far as studio albums go, check out A Picture Of Nectar next. It's similar to Rift but a bit more eclectic. Or maybe Story Of The Ghost if you've heard that one already. It's got a lot of their funky stuff on it. (SOTG is the album they're recording in the studio scenes of Bittersweet Motel).
Phish are fantastic background music cus they're the kind of band that works both when you're paying close attention but also when you're not. It's super easy to let a show just play in the background as you go about whatever else you're doing.