Build a DAQ system for about $30
Free LabView drivers let you use the Arduino hardware as a data-acquisition system.
The free LArVa sample Simple Graph Application installer, available at www.angstromdesigns.com/larva/download, includes the driver, LabView source code, an executable file, and support files. You can use the LabView source code as a starting point for all sorts of projects, including data acquisition, temperature monitoring and control, PWM motion control, and much more. To get users started, Angstrom Designs has also provided application notes on voltage and temperature data acquisition (www.angstromdesigns.com/larva/application-notes).
With a 16 MHz, 8-bit, Atmel microcontroller at it's core, Arduino isn't right for high-end test-and-measurement applications. With solid features and an affordable price, however, it meets the needs of many projects. It's too soon to tell, but Arduino may mark the introduction of open source hardware into professional test and measurement.