For Hondas: the DOHC Vtec heads, and H22/23 heads off preludes would probably be most requested.
A lot of guys don't run Hondas though... there's a fair share of people who run the Zetec engines from the ZX2/Focus, the 20/22R, 2JZ and 4AG engines from Toyota, and then the Nissans, which I admit to being none to familar with. Rotaries are also popular, but thats an entirely different process.