I use Plasti Dip for a lot of tool handles including old pliers that have had their grips worn off. It dries out as a dull/matte version of the way Channellock brand pliers feel, and that was exactly what I wanted so it is perfect for what I need. It does add some thickness though so if it needs to fit a sheath that grips the handle, it might not be the best option. The coating could also rub off after continuous rubbing against the sheath. It does stick well to wood though.
For wood handles what I use is cheap Rustoleum lacquer. A couple of coats of it make the knife handles a little nicer looking too, while making it tacky to the touch. I did it to this "Old Hickhart" handle and it has turned out great. It is much more grippy; enough to convince me to not add the finger grooves I had considered adding to improve its grip. I can't recall if I added any stain but I doubt it. It really brought out the color in the wood though.
Below it is an as-is from factory butcher knife for comparison.
Note- I didn't let the lacquer dry quite enough, so when I put it back in its sheath the leather decided to stick to the lacquer and made the forward-half of the wood more dull. It looked horrible when I first saw it, but it made it even more grippy, so I'm not complaining!
S.Alexander's idea is great, checkering would add a good look to any wood handled knife, and not require any wait time after applying a finish. Just be careful though, I've heard of gun nuts, after buying a checkering tool, spending hours checkering random wooden objects just for the fun of it.
I'd like to think I wouldn't do that, but then I don't have a checkering tool.. yet..
