I grew up not far from Bay Shore, LI - it's about 30-40 minutes east of JFK airport. Back in the day it wasn't too crowded but it probably is somewhat worse now. The big problem is traffic- getting to and from there - if you're travelling anywhere close to peak hours expect to sit in traffic a while - LI only has three main east-west highways and everyone travels in the same direction on them at the same time.
The good thing about Bay Shore is that it's close to some very good fishing. The local marina is pretty big (used to catch snappers by the dozens from the docks there as a kid), and it's close to one of the main access routes into the fire island beaches (robert moses causeway) which will take you right past Captree which has another marina where most of the party boats / charters run out of , along with a pier (never fished that pier as a kid but I've heard it's a good spot). Past Captree is the main route the locals take to get to the beach (traffic all morning on sunny weekend days unless you get out early). An alternate to fighting traffic to get to the beaches, you'll be a few miles away from Hecksher state park along the southern state parkway- there is a boat slip there, and some beach sopts on the bay (can't get a car on the beaches here, but there's parking fairly close to the water - I'd try fsihing the beach right next to the outlet from the boat ramp area- if I remember correctly, bait tends to congregate there as long as there isn't too much boat traffic).
Map of Bay Shore area-
http://maps.google.com/?ie=UTF8&ll=40.686886,-73.241386&spn=0.166094,0.275688&t=h&z=12&om=1Close up of the marina-
http://maps.google.com/?ie=UTF8&ll=40.714867,-73.241816&spn=0.020753,0.034461&t=h&z=15&om=1Marina and fishing pier at Captree State Park
http://maps.google.com/?ie=UTF8&ll=40.641809,-73.253607&spn=0.005194,0.008615&t=h&z=17&om=1Hecksher State Park (baot slip is at the north end of the lagoon in the lower left, easiest walk to beach spots is the parking lot just SSE of that, you'll get bathers in the area, but rarely anywhere near the small channel to the boat slip)-
http://maps.google.com/?ie=UTF8&ll=40.706148,-73.163023&spn=0.020756,0.034461&t=h&z=15&om=1Anyway, the further east you go on long island, the less crowded. The fire island beachfront areas are a different story- the main public beaches are always crowded, but once you get a little off the beaten path the crowds tend to dissappear quickly.
