Best low power low cost ARM Cortex-M family part

I would like to help my clients move off PIC. Many seem to like the low cost of entry, use it to get started, and then come to us asking us to finish. The PIC platform is not the best for what they need...
Small off-the-shelf small ARM module (15mmx25mm or less)?

We are looking for off-the-shelf small ARM module (15mmx25mm or less) with the following specs: - single core >= 100MHz is OK >= 256k RAM >= 256kb ROM >= 2mbit flash - battery charging circuit - uart...
ARM cortex M4

Which Linux version used for ARM cortex M4 ?? and how to install this linux version on TDA3x from Texas instruments ??
Are CMSIS drivers for Flash portable on all Cortex M0(vendor independent)?

I am writing open source easy to use top level Flash drivers which are portable to use on all Cortex M0 devices (vendor independent). So I was thinking of using CMSIS flash drivers as my low level block...
Cortex R

Dear all I want to use ARM Cortex R7,R8,R52. what are development board can i use ? Thank you for your time.