My whole problem with the whole Arduino universe is the price. You essentially pay an extremely large markup for the libraries and community. There are other much cheaper developer platforms out there, e.g. TI's MSP430 launchpad (essentally a $4 development board with a built-in emulator) and the corresponding community ww.43oh.com, but you are much closer to the hardware. So the learning curve is steeper, but you probably going to learn much more.
Another option is the Discovery platform by ST, a very capable ARM platform. The platform you choose will be determined by what you want to do, i.e. turning LEDs on and off you will go for a simple microcontroller e.g. the MSP430; building an IMU for a quadrocopter you will probably need to go for an ARM-like device.