There's not much secret left in the sauce for the iPad's A4 chip - it's a faster, customised version of the chip in the iPhone 3GS. But the recipe probably comes from a tiny chip design firm Intrinsity.
The informed speculation is that Intrinsity's custom ARM chip, Hummingbird, is in fact the basis for the A4 inside of the iPad. The name Intrinsity might sound familiar, since it was rumoured, but not confirmed, Apple had acquired the ARM chip design firm, which specialised in seriously speeding up ARM chips without horribly pillaging battery life.
Well, now Apple's confirmed to NYT that it's true, Intrinsity has been bought by Apple. So the obvious expectation is to keep seeing faster, stronger, custom ARM chips inside of Apple products - like the next iPhone - though what'll be interesting is what they'll be cooking up for Apple in the next couple of years. [NYT]