Add free map your website through this step-by-step tutorial.

No API key needed.

Source Code:

<div id="map" style="top: 0; left: 0; bottom: 0; right: 0; position: fixed;"></div>
Add div #map in your html body. 
<script src="http://www.openlayers.org/api/OpenLayers.js"></script>
Add OpenLayers.js javascript library to html document end of [/body]. 
var lat            = 60.230506;
var lon            = 24.847194
var zoom           = 10;
Initialize variables. 
var fromProjection = new OpenLayers.Projection("EPSG:4326");   // Transform from WGS 1984
var toProjection   = new OpenLayers.Projection("EPSG:900913"); // to Spherical Mercator Projection
var position       = new OpenLayers.LonLat(lon, lat).transform( fromProjection, toProjection);
Transform coordinates EPSG position. 
var map = new OpenLayers.Map("map");
Add new OpenLayers map to div by id #map. 
var mapnik = new OpenLayers.Layer.OSM();
map.addLayer(mapnik);
Add OpenStreetMap background to layer. 
var markers = new OpenLayers.Layer.Markers( "Markers" );
map.addLayer(markers);
markers.addMarker(new OpenLayers.Marker(position));
Add new markers to position you created. 
map.setCenter(position, zoom);
And finally center map to your created position. Whole html file looks like this: 
<!DOCTYPE html>
<html>
	<head>
		<title>OpenLayers Example</title>
		<meta charset="utf-8" />
	</head>
	<body>
		<div id="map" style="top: 0; left: 0; bottom: 0; right: 0; position: fixed;"></div>
		<script src="http://www.openlayers.org/api/OpenLayers.js"></script>
		<script>
			var lat            = 60.230506;
			var lon            = 24.847194
			var zoom           = 10;
			var fromProjection = new OpenLayers.Projection("EPSG:4326");   // Transform from WGS 1984
			var toProjection   = new OpenLayers.Projection("EPSG:900913"); // to Spherical Mercator Projection
			var position       = new OpenLayers.LonLat(lon, lat).transform( fromProjection, toProjection);
			var map = new OpenLayers.Map("map");
			// Add OpenStreetMap to layer
			var mapnik         = new OpenLayers.Layer.OSM();
			map.addLayer(mapnik);
			// Add markers to layer
			var markers = new OpenLayers.Layer.Markers( "Markers" );
			map.addLayer(markers);
			markers.addMarker(new OpenLayers.Marker(position));</p>
			map.setCenter(position, zoom);
		</script>
	</body>
</html>