There are more powerful, EXPENSIVE tools, but we're sure you'll find the Saleae Logic Analyzer to be a convenient, capable, price-effective!
The Parallax USB Oscilloscope is a portable, lightweight oscilloscope that features screen capture, cursors, and many other useful features.
IKA Logic's SCANALOGIC-2 PRO is a small, powerful 4-channel logic analyser with features not found elsewhere on a device this affordable.
This is a powerful 16 channel logic analyzer comes in a sleek black anodized aluminum package from Saleae Logic. Download the free Logic analysis software and check out the stream-line and simple user interface. The software even matches the beauty of the hardware design.