Yes, with the advent of DisplayPort, the latest iMacs are now capable of running displays with the typical 30" resolution...all prior iMacs were limited to 1920x1200, which is a 24" or so.
To run a 30" monitor at its native resolution, however, you will need to buy the $100 Dual-link DVI to Mini-DisplayPort adapter from Apple. Depending on how far back people are sitting from this thing, you may be better off just picking up a 30-40" HDTV, which will be cheaper than a 30" monitor and wouldn't need the $100 adapter (just a cheaper one).