i am currently using the asus p4s333 mobo, its a microatx motherboard that still has 5pci slots on it. It uses the sis 645 chipset, with agp 4x, ddr333 support, nothing hugely fancy, but its a very nice clean little motherboard, which has a standard molex plug on it to provide the extra juice for the p4, so u dont need a new power supply, or hunt for the converter to that damn atx12v plug
Its a hell cheap board too, like 145 bucks Australian (so about 70 american).
Very nice board, and i think you can get the p4s533 as well which is the board rated a bit higher (altho the p4s333 will do 533 fsb p4's).
As for overclockability, i think that basically as long as you get a northwood processor, you will be able to overclock a long way.
Other than that, for board choice cruise the online dealers and look at the available chipsets, then find out what options they have and what options you want, before you make your choice,
The sheer number of chipsets available dont make it anywhere near as easy as buying an AMD mobo, but just keep your eyes open and the choice will jump out at you sooner or later