I stumbled across this low-cost Atmel ATSAM4S-XPLD development board built around an Atmel SAM4S16C.
As well as the SAM4S16C, it has some LEDs, some QTouch touch buttons, and USB/JTAG.
More expensive than the ST Micro STM32F-Dsicovery boards; but not bad for £11.60+VAT.
The SAM4S16C MCU has:
Flash: 1024 Kbytes
RAM: 128 Kbytes
Timer channels: 6
GPIO: 79
UART/USART: 2/2
ADC: 12bit 16 ch
DAC: 12bit 2 ch
External Bus interface: 8-bit data, 4 chip selects, 24-bit address
HSMCI 1 port/4 bits (High Speed MultiMediaCard Interface)
Package: LQFP100 / BGA100
It runs at 120MHz. It is a Cortex-M4, not Cortex-M4F, so AFAIK it doesn't have floating point hardware of STM32F3/4