Group Dinner Recs in Long Island
How about Argentinian steak house/rodizio? I know there's Luso on Main St. in Smithtown, Cafe Buenos Aires (reserve early!, tres popular!) and Fado in Huntington. This is in western Nassau: http://www.churrasqueira.com/
Blackstones is very good, but expect sticker shock. Stay way frm Mac's in Huntington, it's pretty, expensive and serves food that's below the standard of a good diner.