Hi Ronnie- There are only two zip codes in Costa Mesa, either 92626 which is in the western and northern part of Costa Mesa, and 92627, which has most commonly been referred to as East Side Costa Mesa, and also has a small portion of western Costa Mesa in it as well.
Each zip codes have great neighborhoods, it really just depends what type of home you are looking
for. Eastside is more eclectic, and generally also has higher values becasue of proximity to the ocean, the Back bay, and especially Newport Beach.
The western parts of Costa Mesa were designed more like tract homes, however, there are gems like Mesa Verde, cute starter neighborhoods like Halecrest and College Park, and other great neighborhoods.
Whatever you pick, Costa Mesa is a can't miss for entertainment, ease of access to shops and freeways, and the weather is unbelieveable year round!