I don't spend a lot of time watching videos online, and rarely click on ones people recommend, post of Facebook, or whatnot.
These two are very worth it if you're dealing with the issues they address.
This video on pencil grip may (minorly) change my life. I've had an improper pencil grip since Kindergarten. My teacher worked on it with me for ages, and gave me pencil grips and all that, and eventually gave up. People still sometimes comment on my odd grip.
I tried the (quick, easy) exercises, and the pencil really does just naturally fall into the correct position.
Definitely going to try this with the kids, neither of whom has a correct grip, and I'm also going to see if I can learn to write correctly myself. It'll take some practice, since my muscles aren't used to writing that way. But having a proprioceptive mneumonic should help.
This video about B/D confusion seems to have finally gotten the point across to LemurBoy (and possibly Girl, too). It's aimed at the teachers, and you may want to watch it yourself and determine whether it's something you want your kids watching (Nothing particularly offensive, but I now find Boy saying "No Die Die!" and dissolving into giggles every time he runs across a b or d word...).
Some of his other videos look good, too.