I myself use Adobe Flash 8. I will update one day. I will start to use for pencil tests one of the these programs, Plastic Animation Paper one day I might purchase full version. But its costly :(
Plastic Animation Paper (free version, good way to use this is for pencil tests)
Plastic Animation Paper Download
"Plastic Animation Paper (PAP) is a software package for doing 2D animation. It will allow traditional animators to utilize the powerful and timesaving advantages of computers. "
Pencil - Traditional Animation Software (100% Free)
Pencil - Traditional Animation Software Download
"Pencil is an animation/drawing software for Mac OS X, Windows, and Linux. It lets you create traditional hand-drawn animation (cartoon) using both bitmap and vector graphics. Pencil is free and open source. "
MonkeyJam (100% Free)
Monkey Jam Download
MonkeyJam is a digital penciltest program. It is designed to let you capture images from a webcam, camcorder, or scanner and assemble them as separate frames of an animation. You can also import images and sound files already on your computer. Although it is designed for pencil and paper, MonkeyJam can also be used for StopMotion animation and has several features just for that. Movies created in MonkeyJam can be exported as AVI files.
If you have any questions I can try to answer to the best of my knowledge.