An updated version of SimpleKeychain (original: http://stackoverflow.com/a/5251820/334725) that supports accounts

SimpleKeychain.h

#import <Foundation/Foundation.h>

@class SimpleKeychainUserPass;

@interface SimpleKeychain : NSObject

+ (void)save:(NSString *)service account:(NSString *)account data:(id)data;
+ (id)load:(NSString *)service account:(NSString *)account;
+ (void)delete:(NSString *)service account:(NSString *)account;

@end

SimpleKeychain.m

#import "SimpleKeychain.h"

@implementation SimpleKeychain

+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service account:(NSString *)account {
    return [NSMutableDictionary dictionaryWithObjectsAndKeys:
            (id)kSecClassGenericPassword, (id)kSecClass,
            service, (id)kSecAttrService,
            account, (id)kSecAttrAccount,
            (id)kSecAttrAccessibleAfterFirstUnlock, (id)kSecAttrAccessible,
            nil];
}

+ (void)save:(NSString *)service account:(NSString *)account data:(id)data {
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service account:account];
    SecItemDelete((CFDictionaryRef)keychainQuery);
    [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(id)kSecValueData];
    SecItemAdd((CFDictionaryRef)keychainQuery, NULL);
}

+ (id)load:(NSString *)service account:(NSString *)account {
    id ret = nil;
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service account:account];
    [keychainQuery setObject:(id)kCFBooleanTrue forKey:(id)kSecReturnData];
    [keychainQuery setObject:(id)kSecMatchLimitOne forKey:(id)kSecMatchLimit];
    CFDataRef keyData = NULL;
    if (SecItemCopyMatching((CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
        @try {
            ret = [NSKeyedUnarchiver unarchiveObjectWithData:(NSData *)keyData];
        }
        @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", service, e);
        }
        @finally {}
    }
    if (keyData) CFRelease(keyData);
    return ret;
}

+ (void)delete:(NSString *)service account:(NSString *)account {
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service account:account];
    SecItemDelete((CFDictionaryRef)keychainQuery);
}

@end

This solution is no good for arc projects. See this Stack Overflow post for an arc'ified solution:
http://stackoverflow.com/a/20172496/1071320