The most popular are the PIC series by Microchip, the AVR by Atmel, and the 68HC11 by Motorola . All have a number of high-level languages (C/Forth/BASIC) for cheap or free and simple chip programmers that can be built for under $10.

If the compiling/burning/testing cycle is too tedious, the Basic Stamp and its copycats offer a more integrated approach.