Kinetis K21: 50MHz Cortex-M4 MCU, 512KB Flash, 64KB SRAM, Full-Speed USB, Anti-tamper, 121-MAPBGA
Freescale
Freescale - MK21DX128VMC5
$9.07
Freescale - MK21DX256VMC5
$10.12
Freescale - MK21DN512VLK5
$7.58
Freescale - MK21DX128VLK5
$9.30
Freescale - MK21DX256VLK5
$6.69