VidProk (formerly named 'One To One') lets you preview ffmpeg filters (no more test encodes, yey!). Additionally, it includes a VF cheat sheet which lets you conveniently copy/paste filters.
Some of the video filters include: add noise, color curves, deinterlace, denoise (hqdn3d), deshake, draw box, draw grid, fade in, flip horizontal, flip vertical, gamma, geq - emboss, grayscale, histogram, hue and saturation, mplayer: gamma, brightness, contrast (experimental), negate, pp - deblocking, deringing, auto brightness & contrast, sepia, smartblur, unsharp, vignette, and YUV420P.
The VF cheat sheet is by no means a substitute for ffmpeg's documentation --- so, if the default values do not satisfy you, read the ffmpeg manual.
Here are some screen shots...
'play both (horizontal)':
|filters used: gamma, curves, saturation, unsharp, denoise, deblock, yuv420p|
And finally, 'play both @ pos 0x0': Both source and processed windows are placed on the top left corner (one window obscures the other). Clicking 'toggle' alternates between the source and processed windows. This lets you easily see the differences, especially small differences, between the processed and the source windows.
I know that ffmpeg is a no-joy in the instant gratification department (the somewhat cryptic documentation also doesn't help), but I hope you'll like using this tool.
Youtube demo: http://youtu.be/zgXiGfZlTVo
VidProk is included in 'En Masse ~ batch processor for videos', it is absolutely free, and you can download it here: En Masse ~ batch processor for videos