There is a loop around SUNY Old Westbury, i think its 4 miles, Eisenhower Park, or the LIE Service road (East of Glen Cove Road is better than West of GCR)
The path from Cedar Creek Park (in Seaford - right where the Wantagh Parkway and Merick Rd meet) to Jones Beach that ran along the Wantagh used to be great! They are digging it up right now though. Fingers crossed, I've heard it'll be back in action this summer.