Just noticed this WIRED article about how the NOAA is now providing all their weather data via XML. Forecasts, Current Observations, and more are available. There’s even a SOAP interface! Way to go NOAA.
Great timing, since I just finished the first pass on my Quicksilver Weather Plugin. My plugin parses the raw METAR data which is nothing more than space-delimited text. All the data is positional and requires using lookup tables to make it meaningful. Also, my parsing was pretty brute-force as there is no built-in support for Regular Expressions in Cocoa/Objective-C. So, now, instead of a custom (and fragile) parser, I can use the standard (and self-describing) XML feeds. They even include suggested icons!