What program can I used for making screencaps?

I have some videos off my camera that I want to make stills out of. The videos are cool but the stills would be awesome to have in mid-action. What are good (and safe) programs that could be used? Also, I know that some require other installments, so any of the programs recommended can you tell me if they require any additional programs that I would need to have (any plug-ins, etc).