At first Java was considered the ultimate sandboxed client language, though it ended up going in a different direction. Javascript was strictly for silly animations and promotional winky blink until AJAX XMLHttpRequest and Javascript the Good Parts. VBScript was a Microsoft Windows centric sideshow for IE junkies.
Don't forget client side form validation as the main pre-AJAX "serious" usage. Often in the sense of "seriously misguided" when there was no corresponding server side validation of course!
