The i850 Chipset
There's not really that much to say about the one and only chipset available for Pentium 4 right now. Basically, i850 has a lot of similarities with i840E. Both chipsets are using a dual-Rambus channel memory architecture, both share Intel's 'hub architecture', both are using the 82801BA aka ICH2 chip for I/O and PCI and both are pretty expensive.
The only difference is the bus to the processor, which is a normal 133 MHz bus for Pentium III in case of i840 and the quad-pumped 100 MHz bus for Pentium 4 in i850. To ensure this paragraph isn't quite as boring to you, I included this funky picture out of one of Intel's fancy presentations: