I use rabbit board RCM2200 (variance of Z80 at high clock) in my project right now. You can find details about this board at
**broken link removed**
The development suite is quite good from many examples on http, ftp, telnet, udp and also TCP/IP. Not so expensive for a set of development board with the board at 256K ram and 256K flash, a prototype board, C language, and many useful examples.