Once I get my current project off my table, I'm going to start working more on the payload for a high altitude balloon launch. Today, I noticed that Paralllax added a nice little atmospheric pressure sensor. It claims to have a range of about 10 mbar to 1200 mbar, which covers pretty nicely the range expected from a balloon launch (wolframalpha claims the atmospheric pressure at 100K feet is around 11mbar). It includes both SPI and I2C interfaces, which make it easy to pair with any microcontroller, and also has a built in thermometer. Very cool.
They have a bunch of other cool sensors too. Bookmarked for later consumption.