The Idea

I'm still thinking about how and what.

1) I want to run a small LCD display showing current temperatures
2) I also want 2 temperature sensors
3) A serial connection to the PC
4) Atleast one fan.

The LCD would use 7? pins
The temperature sensors use 2 digital inputs/outputs
The serial port uses 2 pins(TX/RX)

I am thinking about trying to use PWM to drive the fans. I have seen that some fans have a NTC (temperature probe) so it might be possible to control the speed by pulsing the signal that normally does to the sensor. I'll need to run some tests to see if it could work.

29.6.2003 I have decided to use a PCF8591 (4 port/8Bit ADC, 1port DAC) to provide the analog inputs. Having this running on the I2C bus only needs 2 pins but provides 4 analog inputs and 1 analog output, so the pin requirements now look like this :-
The LCD would use 6 pins
The temperature sensors for up to 4 inputs uses 2 digital inputs/outputs for the I2C bus
The serial port uses 2 pins(TX/RX)
The Fan outputs require 1 pin per fan
(I have tried a simple test - Replacing the NTC on a fan with a switch and it worked as expected) All I need to do is get a Opto isolated switch that I drive from the AVR and the fan speed problem is solved :).

5.9.2003 After looking abit more I found this Mega8 module
I picked up a module from ebay for alot less than the normal price:)
The module supports the following :-
1) 8kB Flash (Program space)
2) 1Kb Ram
3) 20 I/O ports of which
a) 12 are only digital
b) 8 are digital or analog
4) Onboard RS232 driver
5) 16MHz Crystal