They should. For the most part any iPod accessories will work with any iPod/iPhone as long as it has the correct connector (i.e. isn't a shuffle) and physically fits if there's a dock.
Does this mean that the 2G Invisible Shield should fit the 3G iPod Touch?
I've heard conflicting reports on this matter. I feel that since the two models are the same size that the Invisible Shield should still fit but Zagg says that they're waiting until they receive their 64GB model before they confirm that (even though the purchase page says "2nd Gen/3rd Gen"). 😕
Has anyone tried installing an IS on the 3G yet? I'm planning on installing one on the 32GB 3G.