The Arduino microcontroller platform is probably one of the coolest things to happen to microcontroller hobbying in a long, long time. I'd seen them featured on Hack-A-Day performing various silly jobs for their programmer, I just had never taken the time to look into why people were using them or what made them unique. Last week (at the urging of Bre Pettis) I bought the Arduino Duemilanove. Wow.
First of all, the Arduino is an open, "free" (as in beer) platform running atop the plentiful (and cheap) Atmel AVR microcontroller line. The open nature of the platform allows each revision of the platform and IDE to improve. The current 2009 model is very easy to use. The documentation is pretty good and (imo, best of all) it uses the C programming language. This rounds off the learning curve quite a bit since I have more than a couple years working with C-style programming languages. Now I don't have to fool with BASIC or assembly. I really disliked the patty-cake approach that the BASIC Stamp provided (i hate BASIC), it's easy to get bogged down in assembly, and most C-compilers for microcontrollers are well over $200. The BASIC Stamp pales in comparison to the Arduino in just about every category. The Arduino is cheaper, faster, offers libraries and has a much wider audience than the Parallax BASIC Stamp. The PIC and standard AVRs have a relatively steep learning curve and is easy to get buried in the syntax.
The Arduino abstracts quite a bit for you, freeing you up to be creative and rapidly develop whatever interests you.
What's interested me lately is parsing the WWVB atomic clock signal from Ft. Collins, Colorado. Thanks to a C-Max CMMR-6P receiver chip that I got from DigiKey, I have a data stream going right into my Arduino. A little bit-twiddling and voila I now have the exact time and date. I dug up a couple of old HD44780 LCDs and now have the time displayed. Next up will be the addition of a Real Time Clock chip to hold the current time, maybe the addition of temperature and barometric pressure sensors and I'll have a neat little info station. More on that project some other time.
I also bought an Ethernet Shield so maybe I can share my future project(s) on the interwebs. There's so much that is possible, I can't recommend the little microcontroller highly enough. Check 'em out, they're only $30!