You might as well ask if anyone has tried Canadian Dry in Canada!!! (Which goes extremely well with Thai food I've discovered - thanks Ontario!)

Pocari Sweat is probably the best known of the isotonic drinks amongst foreigners (I think it has something to do with the name...), but there's also Suntory's Dakara, DyDo is bringing out Miu - made with deep sea water... mmmm! Thirst quenching!
And there are loads of other similar drinks by various companies that come and go. Aquarius by Coca-cola is easily available and is pretty similar (not as nice as PS though, IMO)

I probably like PS best, and like to alternate between bottles of this, cold green tea (oicha) and water on hot days.

I'm also very fond of Calpis (marketed as Calpico outside of Japan) and really enjoy a bottle of hot steaming calpis on a chilly day.
Also, when I was a child, Calpis was supporting and sponsoring my favourite cartoons (Heidi and Marco) so my feelings for this company are as warm as their winter lemon product can be.

Perhaps you'd like to try vitamin-in - comes in a plastic 'foil' pack and gives you the sensation you're drinking frog-spawn through a straw. Quite nice when you're in the mood for it!