On the Coast there are 3 main clubs-
*There is Largo at Terrigal on Saturday and Wednesday nights. Largo is the one that yy mentioned. Can be good, depends on how big the crowd is. Music is a bit techno
*There is Iguana Joes which is on Friday nights at Gosford on the waterfront. Personally my favourite.
*Then there is Troppo on Saturday nights at the Central Coast Legues Club at Gosford opposite the stadium, it has a reputation of being "sloppo troppo" but is pretty fun. Troppo is awesome on the long weekends on the Sunday night, Queens birthday long weekend was so so so good.
The main thing to remember is to go with a good group of friends and you will have fun no matter what.
Hope this helped