Progress!
Well partially anyway. I received a red LCD panel from ebay. The feature list sounded good. I2C bus compatible ... but no driver. Well CRAP. I spent the entire weekend writing a driver for it. In the end I got it working.
It's currently displaying the Temperature and Humidity from the DHT11 and the Temperature from the DS18B20 (the DHT11 doesn't go below 0 degC which I'm sure some people's scopes do).
Anyway so far I've got these 3 devices working and I've used some 38% of my available program memory. I think I'm going to need to work on my coding efficiency this weekend.