Ah, well it's worth noting that the iPad/iPhone browser doesn't support any plugins at all (from what I've read... I don't have one) or Java, so the only solution is WebGL. But IE doesn't support WebGL, so it requires a plugin or Java (and Java requires the user to have installed Java). Poking around, it appears a lot more internet users have Flash than Java (95% compared to 75%, thinks StatOwl).

There's no universal solution for your client, so you'll need two. WebGL/HTML5 for iPad and iPhone and some sort of plugin for IE users -- Flash seems to make the most sense.

EDIT: I don't actually know if iPad/iPhone support WebGL, but they apparently support HTML5 pretty well, and the conversation thus far seems to imply WebGL is the iPad/iPhone solution.
EDIT2: Looking back at earlier posts, maybe that won't even work for iPad/iPhone, in which case there's no solution.
EDIT3: But maybe sometime soon it will.