Looking for good ZIP Code / Latitude / Longitude table

I've written a nice php/mysql site that let's you search for hospitals and community colleges by zip code. The search is built upon some math that figures out distances by a zip's lat and lon cords. My problem is that my current ZIP table (bout 42,000 rows) seems to be flawed. There are a ton of zip codes round california that have all the same lat and lons. There are other dups as well. So I'm looking for some new data. Does anyone know a good source for this type of info? Thanks, ~ Mike -- http://www.mikezornek.com