How to get values from 'Person or Group' or 'Lookup' field

SPListItem item; 
.... 

// To get value from 'Person or Group' field 
SPFieldUserValue fieldValue = (SPFieldUserValue)item.Fields["Agent"].GetFieldValue((string)item["Agent"]); 

//Sometimes it is possible that the field display name is different that the internal name.. 
// in this case use the internalname
SPFieldUserValue AssignedToValue = (SPFieldUserValue)item.Fields.GetFieldByInternalName("Assign_x0020_to").GetFieldValue((string)item["Assign_x0020_to"]);


//To get value from 'Lookup' field 
SPFieldLookupValue jobValue = (SPFieldLookupValue)item.Fields["Job"].GetFieldValue((string)item["Job"]);