Agregar pin a un mapa

Lo conveniente es crear una nueva clase que llamaremos Pin:
Pin.h

#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>
#import <CoreLocation/CoreLocation.h>

@interface Pin : NSObject{ 
    CLLocationCoordinate2D coordinate;        
    NSString *subtitle;        
    NSString *title;     
}
    
@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;
@property (nonatomic,retain)NSString *subtitle;
@property (nonatomic,retain) NSString *title;
- (id) initWithCoords:(CLLocationCoordinate2D) coords;

@end 

Pin.m
#import "Pin.h"

@implementation Pin
@synthesize coordinate;
@synthesize subtitle;
@synthesize title;

- (id) initWithCoords:(CLLocationCoordinate2D) coords{

    self = [super init];
    
    if (self != nil)
        coordinate = coords;
    
    return self;
}

- (void) dealloc{
    [title release];
    [subtitle release];
    [super dealloc];

}
@end

Luego agregamos al mapa el pin:

CLLocationCoordinate2D pinlocation;
pinlocation.latitude = latitude;
pinlocation.longitude  = longitude;
Pin *pin = [[Pin alloc] initWithCoords:pinlocation];
pin.title = self.tituloSel;
[mapa removeAnnotations:[mapa annotations]];
[mapa addAnnotation:pin];
[pin release];