I've been using flattext for years.
Examples: breeder referral and rescue contact searches. The map-based search uses zip data - you could search by zip code as easily.
Some notes: the flattext site has a script configurator that allows you to tinker with script customization quite a bit. When you're done specifiying stuff it spits out the completed script - which you can further customize somewhat.
It does seem to use a 'web-bug' - a 1px transparent gif that appears to serve to track where the script key is being used - presumably that's to ensure compliance with licensing.