Add a background image to your UINavigationBar.

main.m

#import <UIKit/UIKit.h>
#import "SCClassUtils.h"

int main(int argc, char *argv[])
{
    [SCClassUtils swizzleSelector:@selector(insertSubview:atIndex:)
                          ofClass:[UINavigationBar class]
                     withSelector:@selector(scInsertSubview:atIndex:)];
    [SCClassUtils swizzleSelector:@selector(sendSubviewToBack:)
                          ofClass:[UINavigationBar class]
                     withSelector:@selector(scSendSubviewToBack:)];

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    int retVal = UIApplicationMain(argc, argv, nil, nil);
    [pool release];
    return retVal;
}

SCAppUtils.h

#import <UIKit/UIKit.h>

#define kSCNavigationBarBackgroundImageTag 6183746
#define kSCNavigationBarTintColor [UIColor colorWithRed:0.54 green:0.18 blue:0.03 alpha:1.0]

@interface SCAppUtils : NSObject
{
}

+ (void)customizeNavigationController:(UINavigationController *)navController;

@end

SCAppUtils.m

#import "SCAppUtils.h"

@implementation SCAppUtils

+ (void)customizeNavigationController:(UINavigationController *)navController
{
    UINavigationBar *navBar = [navController navigationBar];
    [navBar setTintColor:kSCNavigationBarTintColor];

    UIImageView *imageView = (UIImageView *)[navBar viewWithTag:kSCNavigationBarBackgroundImageTag];
    if (imageView == nil)
    {
        imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"navigation-bar-bg.png"]];
        [imageView setTag:kSCNavigationBarBackgroundImageTag];
        [navBar insertSubview:imageView atIndex:0];
        [imageView release];
    }
}

@end

SCClassUtils.h

#import </usr/include/objc/objc-class.h>
#import <Foundation/Foundation.h>

@interface SCClassUtils : NSObject
{
}

+ (void)swizzleSelector:(SEL)orig ofClass:(Class)c withSelector:(SEL)new;

@end

SCClassUtils.m

#import "SCClassUtils.h"

@implementation SCClassUtils

+ (void)swizzleSelector:(SEL)orig ofClass:(Class)c withSelector:(SEL)new;
{
    Method origMethod = class_getInstanceMethod(c, orig);
    Method newMethod = class_getInstanceMethod(c, new);

    if (class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)))
    {
        class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    }
    else
    {
        method_exchangeImplementations(origMethod, newMethod);
    }
}

@end

UINavigationBar+SCBackgroundImage.h

#import <UIKit/UIKit.h>

@interface UINavigationBar (SCBackgroundImage)

- (void)scInsertSubview:(UIView *)view atIndex:(NSInteger)index;
- (void)scSendSubviewToBack:(UIView *)view;

@end

UINavigationBar+SCBackgroundImage.m

#import "UINavigationBar+SCBackgroundImage.h"
#import "SCAppUtils.h"

@implementation UINavigationBar (SCBackgroundImage)

- (void)scInsertSubview:(UIView *)view atIndex:(NSInteger)index
{
    [self scInsertSubview:view atIndex:index];

    UIView *backgroundImageView = [self viewWithTag:kSCNavigationBarBackgroundImageTag];
    if (backgroundImageView != nil)
    {
        [self scSendSubviewToBack:backgroundImageView];
    }
}

- (void)scSendSubviewToBack:(UIView *)view
{
    [self scSendSubviewToBack:view];

    UIView *backgroundImageView = [self viewWithTag:kSCNavigationBarBackgroundImageTag];
    if (backgroundImageView != nil)
    {
        [self scSendSubviewToBack:backgroundImageView];
    }
}

@end

UINavigationBarSCBackgroundImage.h

#import <UIKit/UIKit.h>

@interface UINavigationBar (SCBackgroundImage)

- (void)scInsertSubview:(UIView *)view atIndex:(NSInteger)index;
- (void)scSendSubviewToBack:(UIView *)view;

@end

UINavigationBarSCBackgroundImage.m

#import "UINavigationBar+SCBackgroundImage.h"
#import "SCAppUtils.h"

@implementation UINavigationBar (SCBackgroundImage)

- (void)scInsertSubview:(UIView *)view atIndex:(NSInteger)index
{
    [self scInsertSubview:view atIndex:index];

    UIView *backgroundImageView = [self viewWithTag:kSCNavigationBarBackgroundImageTag];
    if (backgroundImageView != nil)
    {
        [self scSendSubviewToBack:backgroundImageView];
    }
}

- (void)scSendSubviewToBack:(UIView *)view
{
    [self scSendSubviewToBack:view];

    UIView *backgroundImageView = [self viewWithTag:kSCNavigationBarBackgroundImageTag];
    if (backgroundImageView != nil)
    {
        [self scSendSubviewToBack:backgroundImageView];
    }
}

@end