What are the "must have" 4E supplements thus far?

[Jhaelen]

I voted Other, i.e. none. I think PHB2 will be the first 'must have' supplement.

So far I have bought Adventurer's Vault, Martial Power, and Manual of the Planes and while they have a lot of neat stuff, I don't consider them essential, yet. This may change once I've been playing 4E for while. Once all four PHBs are out, all of the AVs and Power books will probably turn into must-have's.

By the time we've reached the Paragon Tier, MoTP may become essential.
By the time we've reached the Epic Tier, new Monster Manuals may become must-have's.

I'd have to agree here. But with the specification on 'the first one'. I'm not sure I'll get the Adventurer's Vault II.

Well, I assume, AV2 will contain a lot of items that are designed to work well with the classes introduced in PHB2, so it should be quite useful if you consider getting PHB2.