I heart living in the middle of Long Island and having way too many from which to choose! But I primarily shop in Nassau County, except for the few times I've headed out to the Tanger Outlets in Riverhead (a hike):
Roosevelt Field Shopping Mall Anchor stores include Macy's, Nordstrom's, Bloomingdale's and JC Penney's. Also includes Coach, Ann Taylor, Apple, Dick's Sporting Goods, A&F, Gap, Diesel, Armani Exchange, Kenneth Cole, Hollister, Express, Urban Outfitters, Guess, H&M and a movie theatre and restaurants. I used to live 8 minutes from RF and worked at the Macy's while in school. I love that place. I could find my way around there blindfolded
However, it gets extremely crowded. Everyone and their mother is there on a Saturday afternoon.
Broadway Mall Anchored by Macy's, Target, IKEA and a movie theatre. I'm sad Express just closed. Contains H&M, AE, Old Navy and smaller tweeny-bopper stores. This used to be the mall that the parents used to think was "safe" and would just drop the kids off for a few hours. It was small and then grew in recent years. The mall is still teeming with middle schoolers. It's just convenient for me if I need anything, as it's on the way home from work.
The Mall at the Source Expanded after RF started growing. Includes Fortunoff, Dave & Busters, The Cheesecake Factory, Circuit City, Famous Footwear, Foot Locker, David's Bridal, H&M, Gap and Old Navy. I tend to avoid The Source. Not as large as RF. Parking is horrendous.
Americana Manhasset Also known as the "Miracle Mile." Includes Louis Vuitton, Prada, Oscar de la Renta, Giorgio Armani, Ralph Lauren and Tiffany & Co. People with money shop here
I like to browse.