Similar to Vhoto, StillShot from Macadamia Apps allows you to grab a still photo from a video. While Vhoto automates the process for you, StillShot allows you scroll through the video frame-by-frame and choose the best shot.
StillShot is extremely easy to use. Just open the app, select your video from your video library (StillShot filters out your photos, showing only your video clips) and scroll through the frames. When you find an image you like, hit the "Share" button, and it will be saved in full resolution to your camera roll. You also have the option to post the image to Facebook, share it on Twitter or print it.