What have you found that works the best for dry ends of your hair as a preventative product?

Trimming your hair works the best.

Failing that, since I colour my hair a lot, I love the conditioner that comes in the box with it, (L'Oreal is the best so far). It is by far, the most nourishing conditioner I have ever had in my hair. It's a shame they don't sell it separately.

You can also try hair serums like the ones from Bumble and Bumble (frizz ease or something..) they have silicone in them, which will coat your hair strands and make the split ends "stick" together and look healthy/shiny.