>What's so great about nuclear fusion? If this works does that mean we'll have clean energy without radioactive byproducts?
Yes. Some reactions produce neutrons, but that's more of a 'how do we shield the reactors properly' issue.
>Why is this better than nuclear power plants today?
Because it's several (well, that's an understatement) orders of magnitude more efficient (in theory) and does not require uranium mining. Startup requires an initial energy investment but after this it is self-sustaining.
>Next, assuming we get this working, what material does it require to make it work successfully? And really, what then becomes the bottle neck to producing infinite cheap energy?
Mostly hydrogen and helium isotopes. Since fusion is not a particular, there are several different combinations that can result in exothermic reactions. Helium-3, for example, is known to be present in abundance on the moon. Unfortunately, the kind of reactions that it's involved in kind of suck for various reasons (energy density and production of neutrons) and helium in general is rather difficult to produce anyway.