The New York Mets Clubhouse Store, located in Roosevelt Field Mall in Garden City, is a must for any fan of the Mets and baseball in general. The store has various Mets apparel, memorabilia and novelties. There's a life-sized Mr. Met statue, and there's the obvious jerseys. There are even some jerseys for other teams (think Red Sox and Yankees), because not everybody's a Met fan. The prices beat those in the Mets store in Shea Stadium, and some items are cheaper here than at Modell's. I would recommend taking a look here.
Edit: wrong category: should be placed in Retail Stores - Other