PIC MCUs with nanoWatt XLP Technology for low power embedded applications bring you:
■ Sleep / Power-down current down to 20 nA
■ Brown-out Reset down to 45 nA
■ Watch-dog Timer down to 400 nA
■ Real-time Clock/Calendar down to 500 nA
参考：
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1484
比较新 不知道能不能买到

看你需要.要很低的功耗要软硬兼施才行.

18K，PIC16F193X，都是XLP系列的。

PIC24F16