I keep my freezer stocked with Pedialyte freeze pops during the summer months. They keep me hydrated, and cool. I also drink a lot of Powerade Zero, and Spring Water. As Heiferly said though, Powerade Zero is kind of expensive.
I like the idea of adding salt, and a little fruit juice to ice water! I hadn't thought about that!
I like Powerade Zero (to avoid extra sugar/calories, which I don't need). The downside is that at about $1 per 32 oz bottle, I can easily add $100 or more to my monthly budget if I rely heavily on those, which isn't practical for me. I don't like the taste of plain water, so I'm better about staying hydrated if there's a constant supply of Crystal Light available. I like the regular flavors diluted 50% with water.
Better than that, Kroger has a powdered mix almost identical to Crystal Light but without the neon artificial colors and with more of a sports drink electrolyte/vitamin profile. It's definitely more economical mixing that up by the jug at home than buying bottles of Powerade.
Lastly, when I'm really hurting for sodium, adding salt directly to ice water and masking the taste with a bit of fruit juice does the trick.