http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.publishing.webcontrols.asseturlselector.aspx

Custom asset picker field in SharePoint 2010
http://vamshikgovind.wordpress.com/2010/11/07/assetpicker/

 http://fahadzia.com/blog/2009/11/using-sharepoint-image-picker-to-select-images/

How to: Customize the Asset Picker in SharePoint Server 2010 (ECM)

http://msdn.microsoft.com/en-us/library/ms543215(v=office.14).aspx