Etymotic earbuds. Great sound reproduction, fit in one's pocket with room to spare, and top notch sound isolation (not noise cancellation, sound isolation - no electronics or batteries.)

I've had some "ear reduction surgery" (cancer removal) and could only use the Bose over-the-ear QC1s or -2s (built in fragility in the part connecting the headband to the earcups, a known efficiency) and tried the Etymotics ER6s - a winner!