Use one of the well known map providers like Google Map, Yahoo Map or Microsoft Map APIs. They are easily customizable and you can display your data on their map as you like. I suggest you to use Google Map. Its API is very rich and is growing rapidly (adding new services every now and then). In order to use one of these APIs, you just need to register an API Key and start embedding a map on your site.
Take a look at Google Map API Documentations and samples at
However, if you need to use your own map images (tiles) you can use OpenLayers.
It's an open source library with all basic functionalities of a Map API and also an active community of developers.
Check it at http://www.openlayers.com
However, in my opinion, it's little large and its API is not so developer friendly. There is a reference documentation for all classes and main components, but it may take you some time to become familiar with its terminology (if you have no background in GIS systems).