The AVR series of microprocessors is quickly becoming my CPU of choice. The family has a wide selection of parts, from 8 pin DIPs to large flat packs.
I'm using the Atmel STK500 development kit. It was only $79 from Digikey. The STK500 comes with an excellent assembler/debugger IDE, and supports a wide range of AVR devices and programming modes. Development is quick and easy.
I've also been experimenting with the AVR Butterfly, which is a very inexpensive ($20!), but feature packed AVR device. It can be programmed with WinAVR, and excellent port of  the GNU GCC compiler. The Butterfly is also available from Digikey.

2313Temper8 is an AVR assembly language program that reads up to 8 DS1820/DS18S20 devices connected to Port B pin 2 of an AT90S2313 and calculates the extended temperature for the DS18S20 selected. The software uses the '2313's UART to communicate with a host computer at 9600,8,N,1.

AVR2LCD is an AVR assembly language program  that connects an AT90S2313 to a standard alphanumeric LCD that uses a Hitachi (or equivalent) HD44780 display driver. It only uses three port lines, thanks to a 74HC164 8 bit shift register. Code and schematics are included in the zip file.

AVR Freaks
Atmel AVR Page
AVR-Tutorial  Excellent AVR assembly language projects.
AVR Embedded Microcontroller Resources
AVR Projects by Martin Thomas. Martin has ported the AVR Butterfly application code to avr-gcc. He also has example code.
WinAVR is a port of the GNU GCC compiler. The Windows version comes with Programmer's Notepad, and excellent programming editor.