How to get Object API Name in salesforce through apex code

Through User Interface

To Know Standard Object API Names follow this below link,
http://www.salesforce.com/us/developer/docs/api/Content/sforce_api_objects_list.htm

To Know Custom Object API Names

Go to Setup--> Build --> Create --> Object --> Click the Object Name --> then you will find the API Name.

Through ApexCode

If you want to retrieve object label and API Name via Apex coding means you can use the following code,

01	List<Schema.SObjectType> gd = Schema.getGlobalDescribe().Values();

02

03	Map<String,String> objName = new Map<String,String>();

04	for(Schema.SObjectType f : gd)

05

{

06	if(f.getDescribe().isCustom())

07

{

08	objName.put(f.getDescribe().getLabel(),f.getDescribe().getName());

09

}

10

}

11

12	System.debug('Object Names'+objName);