I figure someone might ask why 0.2C isn't good enough. In a weather situation, especially with things like freezing rain, you want something accurate to at least a tenth of a degree fahrenheit. 0.1c == .18 fahrenheit, so even that is outside the desired range. Ideally, I'd like something that could take advantage of a 0.1% 10k thermistor, but haven't found such a solution yet for the arduino. It may be I'd have to go with a different microcontroller entirely, which would be a shame since the arduino seems like such a newbie friendly way to get into microcontrollers.
Thanks for the info copiertalk. To be honest I'm wary of going with OS stuff, given my experiences with them along with what I've heard from friends who've had even their higher end weather stations. Their stuff tends to have QC issues, are unreliable, and prone to failure. I had my eye on the sparkfun anemometer package but I just want to start out with the basics (temp sensor, pressure sensor, fan aspiration, relative humidity sensor, and possibly a wireless solution for outside siting) to begin with, and then possibly add things like anemometer and rain gauge down the road sometime.