I am definitely not a fan of assembly language programming. When I'm creating interactive art, I want to create art, not have to search through 100 pages of PDF documentation to figure out how to properly configure a register for reading. I don't mind getting paid to solve insanely difficult technical problems, while I like the challenge of hardware tech art, I prefer to actually get it done.
The BASIC Stamps from Parallax are expensive for what you get, which often does not include an analog input. The BASIC interactively programmed RVHE has been discontinued. I'm using one for Sycophant 2, and I have one more. For a board with Ethernet it was a good deal, but I found that it didn't really play well when you tried to send IP packets off of the local subnet.
Recently I have become very interested in the Arduino, available from SparkFun for $31.95. You get 13 digi I/Os, 6 analog ins, it connects to your PC for programming over a USB port, plus it also has an extra serial port on the board (in case you want to add an Xport for IP connectivity). The Arduino is programmed in a C-like high level language. Not only is the development environment free and open source, the board design is open source as well. There is an excellent set of learning materials about the Ardunio from Tod E. Kurt's blog.
A cheaper system is the LogoChip, a PIC 18F2320 programmed with an interpreter for a language based on Logo. It has 12 digi I/O pins and 5 analog input pins, and a UART you can use for a serial connection. You can buy the PIC chip for ~$5 from Newark, then if you have a PIC programmer you can download the free Logo interpreter to the chip. In a free development environment, you write the Logo code and send its tokens to the LogoChip to run. It appears that there is an interactive execution mode as well. Although the LogoChip language is a bit closer to the physical chip hardware, the abstraction is enough to make most programming easy.
My other recent discovery is Processing, "an open source programming language and environment for people who want to program images, animation, and sound." It seems like an interesting counterpoint to Pure Data.
Finally, check out this awesome course at Wichita State University:
Technology: Art and Sound by Design consists of lectures and labs, with a focus on artistic philosophy and its application through technology. In the course, students build circuits and interface them to computers, considering how these might contribute to their own artistic creations.
Engineering students are expected to help Fine Arts students with the technical material covered. Fine Arts students are expected to spark a conversation about how the technical material might be used creatively within their discipline.