I continue to be pleased with the Nucleo boards. I now program flash by drag and drop of the apps .bin file to the Nucleo folder. This does not interrupt the connection to the serial monitor since there is a second STM32F103 that handles the serial monitor, programming flash, and debug.
There is a new NUCLEO-F411RE ($10.33 from Future Electronics). It is faster, 100 MHz, has more SRAM, 128 KB, and 512 KB of flash. There are three SPI controllers, three I2C controllers, and three UARTs.
I have tested the ADC on these boards and it is at least 50 times faster than the Uno, 2.4 MSPS. The 12-bit ADC seems to be very accurate.
I have almost finished porting a new FAT32/FAT16/FAT12 generic file system to the STM32. I plan to support SD on SPI, SD on 4-bit SDIO, and USB flash drives. 4-bit SDIO should be very fast since it should run at 50 MHz. on the F411.
I also bought a 32F429IDISCOVERY board for $33.60 http://www.st.com/web/catalog/tools/FM116/SC959/SS1532/PF259090
. 256 KB internal RAM, 8 MB external SRAM, 2 MB flash, 180 MHz clock, 2.4" TFT touch screen.
The external SRAM has a 16-bit data bus and runs at 80 MHz. Its three 12-bit ADCs can run in interleaved mode to digitize a signal at up to 7.2 MSPS.
Edit: Just checked and Future electronics now sells the 32F429IDISCOVERY for $24.00, about the same as an Uno.