I'm a strong Arduino advocate, that thing rocks. Very easy point of entry into embedded systems and provides a great balance between simplicity and capability. The interface is easy enough to use that you can learn to write a simple program in under an hour, and in college I wrote a real-time operating system that ran on an Arduino*.
If I'm trying a new microcontroller and I can't use the Arduino IDE, that's a dealbreaker for me.
*it was hard and I did not enjoy it