My first foray into microcontrollers was with the PIC16F84 using Michael Covington's "No Parts PIC Programmer." I built one when I learned I could drive it from Linux. I had a good time playing with it. However, I thought the architecture was a little odd but, at the time I understood that most microcontrollers had such quirks.
I stumbled upon the Atmel line of microcontrollers purely by accident. I was doing a google search for programmable logic that could be programmed from Linux and Guido Socher's web page came back as a hit. Although it didn't actually having anything to do with programmable logic it caught my eye. After reading it for a bit my interest rose and I started doing more research. The big thing that attracted me was the ability to do In Circuit Programming (ISP) without having to generate the 12.x volts necessary to program the flash. That meant I did't have to either build that into my designs or pop the chip out and into the programmer every time I wanted to change anything.
Programming is a very iterative process. As far as I am concerned getting it right the first time went away with time-shared mainframes and punch cards and good riddance to it. So, for me, removing this step is a big thing. I promptly downloaded the PDF for the AT904433, the predecessor of the mega8l that we have been using in the local robotics club. I was instantly hooked by its clean architecture and capabilities. I snagged some from digikey and was off.
A short time later a discussion came up if any members of the club wanted to try and develop some of group mind around a processor for robotics projects. At the time the PIC seemed to be a wise choice. I brought up the AVR and within a short time several people thought it was worth trying.
My preferred programming environment is in some variant of UNIX (Linux is what I use most at home) and in C. I know assembler but these days modern compilers are so good that they can produce code that rivals hand-crafted assembler. I was ESPECIALLY delighted to learn that the AVR line of microcontrollers is well supported by gcc, a world-class open-source compiler that I am very, very familiar with. This is a sandbox I am extremely happy playing in.
If gcc isn't your thing the FREE Avr studio for windows is available from Atmel. Or, you can use the Bascom BASIC environment or you can give Codevision a try. Go here for more information on these alternatives.
Update Tue Aug 17, 2004
HOLY MACKEREL! After having written thousands of lines of code for the AVR processors I can't go on enough on how outstanding the experience has been. No, I don't work for Atmel. However, I realized how it's been when I looked back on the projects I have stored on my server. When I summed up how much stuff I have produced for just one of my hobbies (and I have many) I was amazed. Not only that the list of potential projects is as long as my arm (and I have very long arms). The people who put together avr-libc should be commended for their work and Atmel has, as far as I am concerned, a real winner here. Nice job, people. I look forward to sharing many of my projects with you assuming I can tear away from development and update my web pages!